groupBy not working in latest version

Hello folks, many thanks for a very nice work!

I'm completely pissed off groupBy.

I have .grenrc.json (cause there are no examples available how to use yaml):

```
{
"dataSource": "milestones",
"prefix": "",
"groupBy": {
"Bug Fixes:": [ "bug","minor" ],
"Refactoring": ["refactoring"],
"Major features": ["feature", "major"]
},
"milestoneMatch": "(Milestone {{tag_name}})",
"changelogFilename": "CHANGELOG3.md"
}
```

Whenever I call gen changelog --override I have exactly the same output:

```
## v1.0.0 (13/11/2020)
- [**refactoring**] Refactor release path and impact analysis to DTOs [#106](https://github.com/tillias/microservice-catalog/issues/106)
- [**documentation**][**major**] Visual regression tests with percy.io [#103](https://github.com/tillias/microservice-catalog/issues/103)
- [**bug**][**minor**] Clear selection in dependency dashboard after microservice deletion [#100](https://github.com/tillias/microservice-catalog/issues/100)
- [**documentation**] Prepare e2e tests with cypress [#96](https://github.com/tillias/microservice-catalog/issues/96)
- [**feature**][**minor**] Display status and team name for microservice dialog(s) [#90](https://github.com/tillias/microservice-catalog/issues/90)
- [**feature**][**minor**] Edit microservice button [#89](https://github.com/tillias/microservice-catalog/issues/89)
- [**documentation**] k8s deployment scripts [#88](https://github.com/tillias/microservice-catalog/issues/88)
- [**feature**][**major**] Dependency dashboard legend [#86](https://github.com/tillias/microservice-catalog/issues/86)
- [**feature**][**minor**] Swap nodes in create dependency dialog [#84](https://github.com/tillias/microservice-catalog/issues/84)
- [**feature**][**major**] Impact analysis [#79](https://github.com/tillias/microservice-catalog/issues/79)
- [**feature**][**minor**] Build docker image and push from circle-ci [#76](https://github.com/tillias/microservice-catalog/issues/76)
- [**feature**][**minor**] Migrate to circle-ci [#74](https://github.com/tillias/microservice-catalog/issues/74)
- [**feature**][**major**] Duplicated dependencies validation [#71](https://github.com/tillias/microservice-catalog/issues/71)
- [**bug**] Name for target node in release path is not displayed [#70](https://github.com/tillias/microservice-catalog/issues/70)
- [**feature**][**minor**] Delete dependency & microservice using hotkey [#69](https://github.com/tillias/microservice-catalog/issues/69)
- [**bug**][**minor**] Translation for custom validation errors [#68](https://github.com/tillias/microservice-catalog/issues/68)
- [**feature**][**minor**] SonarCloud code coverage issue [#65](https://github.com/tillias/microservice-catalog/issues/65)
- [**feature**][**minor**] Create dependency by selecting multiple nodes [#61](https://github.com/tillias/microservice-catalog/issues/61)
- [**feature**][**major**] Build and visualize release path for particular microservice [#57](https://github.com/tillias/microservice-catalog/issues/57)
- [**feature**][**minor**] Remember start dependency when creating new one [#56](https://github.com/tillias/microservice-catalog/issues/56)
- [**feature**][**major**] Dependency validation [#54](https://github.com/tillias/microservice-catalog/issues/54)
- [**feature**][**minor**] Delete dependency from dashboard screen [#53](https://github.com/tillias/microservice-catalog/issues/53)
- [**documentation**] Update home page and create gitter chat [#50](https://github.com/tillias/microservice-catalog/issues/50)
- [**bug**] Search box looses its content when accordion panel is collapsed [#47](https://github.com/tillias/microservice-catalog/issues/47)
- [**feature**][**major**] Actions menu for dependency dashboard [#45](https://github.com/tillias/microservice-catalog/issues/45)
- [**documentation**][**feature**][**minor**] Try with PWD badge [#43](https://github.com/tillias/microservice-catalog/issues/43)
- [**documentation**][**feature**][**minor**] Custom port for Spring Boot App [#41](https://github.com/tillias/microservice-catalog/issues/41)
- [**documentation**][**minor**] Docker compose for rapid use-cases demo [#39](https://github.com/tillias/microservice-catalog/issues/39)
- [**feature**][**minor**] Feature flags [#38](https://github.com/tillias/microservice-catalog/issues/38)
- [**feature**][**minor**] Add CI link to microservice [#32](https://github.com/tillias/microservice-catalog/issues/32)
- [**feature**][**minor**] Reset search criteria using icon or button [#30](https://github.com/tillias/microservice-catalog/issues/30)
- [**bug**][**minor**] Localization for search box & direction selectors [#29](https://github.com/tillias/microservice-catalog/issues/29)
- [**feature**][**major**] Create dependency from dependencies dashboard [#27](https://github.com/tillias/microservice-catalog/issues/27)
- [**feature**][**major**] Create microservice from dependencies dashboard [#26](https://github.com/tillias/microservice-catalog/issues/26)
- [**feature**][**minor**] Display microservice description in dependency view on mouse over [#23](https://github.com/tillias/microservice-catalog/issues/23)
- [**bug**] Dependency graph is incorrect, missing edges [#20](https://github.com/tillias/microservice-catalog/issues/20)
- [**feature**][**minor**] Setup sonar-qube [#18](https://github.com/tillias/microservice-catalog/issues/18)
- [**feature**][**major**] Search box for dependency view [#17](https://github.com/tillias/microservice-catalog/issues/17)
- [**feature**][**major**] Multi-field search criteria (advanced search) [#16](https://github.com/tillias/microservice-catalog/issues/16)
- [**feature**][**minor**] Generate long-term heroku token for travis-ci [#14](https://github.com/tillias/microservice-catalog/issues/14)
- [**feature**] Better handling of big images [#13](https://github.com/tillias/microservice-catalog/issues/13)
- [**feature**] Improve travis-ci build [#11](https://github.com/tillias/microservice-catalog/issues/11)
- [**feature**] Extract dashboard card into separate comoponent [#10](https://github.com/tillias/microservice-catalog/issues/10)
- [**feature**] Bundle some test images for dev profile [#7](https://github.com/tillias/microservice-catalog/issues/7)
- [**feature**] Microservice custom details component [#6](https://github.com/tillias/microservice-catalog/issues/6)
- [**feature**] Search field [#5](https://github.com/tillias/microservice-catalog/issues/5)
- [**feature**] Configurable data source [#3](https://github.com/tillias/microservice-catalog/issues/3)
- [**feature**] Visualize dependencies between microservices [#2](https://github.com/tillias/microservice-catalog/issues/2)
- [**feature**][**minor**] Configurable image source [#1](https://github.com/tillias/microservice-catalog/issues/1)
```

There is no grouping at all (

Can you please advise what I'm doing wrong?

Reproduce the report with the shown .grenrc.json configuration and the `gen changelog --override` command. Trace the changelog generation entry point and the handling of `groupBy`, then compare the output with the requested category grouping. Done means matching entries are emitted under the configured group headings.

索引モデルが issue の本文から書いたものです。