fix: correctly increase version for "pre" versions

[fjcasternao]

We are using this plugin to bump versions every time we release using our CI. It happens for us that we use to create prereleases for QA to test and it can happen that we have several preminors before reaching the final one.

We realised, there were some issues with the version calculation on this specific scenario, so wanted to submit the fix.

Failing test reflecting the issue is the one on line 130, but the fix was also affecting some of the existing tests so I had to modify them also.

[wraithgar]

The existing tests are correct, I'm not sure what this change is trying to fix.

1.2.0-0 is the pre-release for 1.2.0 not 1.2.1. If I bump 1.2.0-0 by a patch I should go up to 1.2.0. There is a significant amount of prior discussion on this in these PRs:

• fix: incorrect results from diff sometimes with prerelease versions #546
• feat: allow identifierBase to be false #548

[fjcasternao]

Maybe I am wrong, but to me, 1.2.0-0 is a preminor bump from let’s say 1.1.9

in #546 on your last comment you mention this 1.2.0-pre inc: 1.2.1-0 diff: prepatch that I guess is consistent with my approach here