gren changelog vs gren changelog --generate inconsistency

After fiddling with the PRs for #140, I came across something that might be an inconsistency in the code.

Running:

gren changelog --include-messages=all --override

Generates `CHANGELOG.md` (with all releases) these lines (before the fix):

## v1.1.0-beta.0 (01/03/2018)
- [1.1.0-beta.0](https://api.github.com/...) - Author Authorson

After changing the template in the global scope for `templateCommits`, I rerun:

gren changelog --include-messages=all --override

Providing the same result. Which has not the updated URLs.

But if I run:

gren changelog --include-messages=all --override --generate

I get the `CHANGELOG.md` with the updated template:

## v1.1.0-beta.0 (01/03/2018)
- [1.1.0-beta.0](https://github.com/...) - Author Authorson

Is this intended, or a bug?

Reproduce the two commands shown in the issue: gren changelog --include-messages=all --override and the same command with --generate. Trace the changelog generation path and template handling to determine why the updated URLs differ; done when both modes consistently apply the selected template, with coverage for the reported commands.

Scritto dal modello di indicizzazione a partire dal testo della issue.