`template` doesn't impact output for some fields

We have a file `.grenrc.js` generated from `gren int`

After adding a template object it looks like this:

```
module.exports = {
"dataSource": "milestones",
"prefix": "n",
"groupBy": "label",
"milestoneMatch": "{{tag_name}}",
"changelogFilename": "CHANGELOG.md",
"template": {
commit: ({ message, url, author, name }) => `- [${message}](${url}) - ${author ? `@${author}` : name}`,
issue: "- {{labels}} {{name}} [{{text}}]({{url}})",
label: "[**{{label}}**]",
noLabel: "closed",
group: "\n#### {{heading}}\n",
changelogTitle: "# Changelog\n\n",
release: "## {{release}} ({{date}})\n{{body}}",
releaseSeparator: "\n---\n\n"
}
}
```

When I change values for `issue`, `label` or `group`, the `CHANGELOG.md` file is still generated from the original template. Changing values for `release` and `changelogTitle` do impact though.

使用生成的 .grenrc.js 重现问题，并检查生成 CHANGELOG.md 时其模板值的应用方式。比较 issue、label 和 group 与 release 及 changelogTitle 的处理方式，然后验证更改每个值都会改变相应的输出。

由索引模型根据 Issue 内容生成。