Add sort! and minmax to Performance/CompareWithBlock

[vlad-pisanov]

Performance/CompareWithBlock currently only looks at sort, min and max usage.

This PR adds support for sort! and minmax methods which behave the same way.

# bad
arr.minmax { |a, b| a.foo <=> b.foo }
arr.sort!  { |a, b| a.foo <=> b.foo }

# good
arr.minmax_by(&:foo)
arr.sort_by!(&:foo)

Comparison:
               minmax_by:  1513625.0 i/s
               minmax:     1178249.9 i/s - 1.28x  slower

Comparison:
               sort_by!:    21368.8 i/s
               sort!:       13662.7 i/s - 1.56x  slower

---

Before submitting the PR make sure the following are checked:

• The PR relates to only one subject with a clear title and description in grammatically correct, complete sentences.
• Wrote good commit messages.
• Commit message starts with [Fix #issue-number] (if the related issue exists).
• Feature branch is up-to-date with master (if not - rebase it).
• Squashed related commits together.
• Added tests.
• Ran bundle exec rake default. It executes all tests and runs RuboCop on its own code.
• Added an entry (file) to the changelog folder named {change_type}_{change_description}.md if the new code introduces user-observable changes. See changelog entry format for details.

[koic]

Thanks!