PL-19 ⁃ Remove case-sensitive restriction for semantic release keyword

[koalamango]

For example, we should be able to use keyword FIX:/fix:/Fix: and not limited to fix on semantic release

[ayanozturk]

There is an issue created to address this problem but currently pending with a long time of inactivity
semantic-release/commit-analyzer#3

I'm going to follow other issue thread and close this one.