Update Style/Semicolon to add autocorrection

[dvandersluis]

I noticed that Style/Semicolon doesn't do autocorrection, so this adds basic auto-correction (replaces semicolons between statements with a new line, indentation will be fixed by other cops).

A small autocorrection conflict between this and Style/SingleLineMethods is prevented by adding that to autocorrect_incompatible_with (which we need to document somewhere because I can never remember what it's called 😬).

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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.

[bbatsov]

A small autocorrection conflict between this and Style/SingleLineMethods is prevented by adding that to autocorrect_incompatible_with (which we need to document somewhere because I can never remember what it's called 😬).

Sounds like we need one more PR for this! ;)

Good work!