Probably bug with --tag-prefix

[KeNaCo]

So I was playing little bit with the --tag-prefix option:

~/Dev/auto-changelog/sandbox$ git log
commit 613ee7574a1c678a6995fda2756a2ff39f7e62e3 (HEAD -> master, tag: 2.0.0)
Author: Ken Mijime <kenaco666@gmail.com>
Date:   Sat Dec 19 00:56:54 2020 +0100

    feat: Add file PRO-1

commit 3cd47a8e2943697e8917e806f2d3653f87984c6c
Author: Ken Mijime <kenaco666@gmail.com>
Date:   Sat Dec 19 00:30:21 2020 +0100

    feat(module): Add file #1

commit 05d3372f6f6605e98654d66e96793e4e412ec956 (tag: v1.0.0)
Author: Ken Mijime <kenaco666@gmail.com>
Date:   Fri Dec 18 23:43:06 2020 +0100

    feat: Add file #1
  kenaco  master:
~/Dev/auto-changelog/sandbox$ npx auto-changelog --tag-prefix "v"
auto-changelog: 1 kB written to CHANGELOG.md
  kenaco  master:
~/Dev/auto-changelog/sandbox$ cat CHANGELOG.md 
### Changelog

All notable changes to this project will be documented in this file. Dates are displayed in UTC.

Generated by [`auto-changelog`](https://github.com/CookPete/auto-changelog).

### [2.0.0](https://github.com/KeNaCo/auto-changelog/compare/v1.0.0...2.0.0)

> 19 December 2020

- feat: Add file PRO-1 [`613ee75`](https://github.com/KeNaCo/auto-changelog/commit/613ee7574a1c678a6995fda2756a2ff39f7e62e3)
- feat(module): Add file #1 [`3cd47a8`](https://github.com/KeNaCo/auto-changelog/commit/3cd47a8e2943697e8917e806f2d3653f87984c6c)

#### v1.0.0

> 18 December 2020

- feat: Add file #1 [`05d3372`](https://github.com/KeNaCo/auto-changelog/commit/05d3372f6f6605e98654d66e96793e4e412ec956)
  kenaco  master:
~/Dev/auto-changelog/sandbox$ npx auto-changelog --tag-prefix "v1"
auto-changelog: 1 kB written to CHANGELOG.md
  kenaco  master:
~/Dev/auto-changelog/sandbox$ cat CHANGELOG.md 
### Changelog

All notable changes to this project will be documented in this file. Dates are displayed in UTC.

Generated by [`auto-changelog`](https://github.com/CookPete/auto-changelog).

#### 2.0.0

> 19 December 2020

- feat: Add file PRO-1 [`613ee75`](https://github.com/KeNaCo/auto-changelog/commit/613ee7574a1c678a6995fda2756a2ff39f7e62e3)
- feat(module): Add file #1 [`3cd47a8`](https://github.com/KeNaCo/auto-changelog/commit/3cd47a8e2943697e8917e806f2d3653f87984c6c)
- feat: Add file #1 [`05d3372`](https://github.com/KeNaCo/auto-changelog/commit/05d3372f6f6605e98654d66e96793e4e412ec956)
  kenaco  master:
~/Dev/auto-changelog/sandbox$ npx auto-changelog --tag-prefix "2"
auto-changelog: 1 kB written to CHANGELOG.md
  kenaco  master:
~/Dev/auto-changelog/sandbox$ cat CHANGELOG.md 
### Changelog

All notable changes to this project will be documented in this file. Dates are displayed in UTC.

Generated by [`auto-changelog`](https://github.com/CookPete/auto-changelog).

#### v1.0.0

> 18 December 2020

- feat: Add file #1 [`05d3372`](https://github.com/KeNaCo/auto-changelog/commit/05d3372f6f6605e98654d66e96793e4e412ec956)
  kenaco  master:

In the first case, it's like completely ignoring the prefix option. In the two following examples, it filters out the exact opposite of what I want with the prefix.
Is it a bug or just me not understanding how this option supposed to work? In the latter case, can you please explain?

[cookpete]

The option description admittedly isn’t great. --tag-prefix is for when your version tags are prefixed by something, like myproject-2.0.0, so that the 2.0.0 can be parsed correctly.

See #22 for details of the problem that it intends to solve.