Attempt to point out known problems in changelog lines

[dblock]

For example in https://github.com/ashkan18/graphlient/pull/45/commits/dbdb6797caa64289746e958b7ce3b0bbfa5fb0b2 the developer has no idea that the changelog is missing a period.

[jonallured]

My approach to this problem on commit_lint was to define a series of checks that can each give feedback:

https://github.com/jonallured/danger-commit_lint/blob/master/lib/commit_lint/plugin.rb#L80-L88

For instance, here's the one for ending with a period:

https://github.com/jonallured/danger-commit_lint/blob/master/lib/commit_lint/subject_period_check.rb

[dblock]

The example in https://github.com/ruby-grape/grape-swagger/pull/764#issuecomment-570656824 could definitely point out that a colon is missing.