Sort analyzed file alphabetically

[pocke]

The order of files that RuboCop analyzes is not fixed. Because RuboCop uses Dir.glob and the order of the Dir.glob is not fixed.

Note that the pattern is not a regexp, it’s closer to a shell glob. See File.fnmatch for the meaning of the flags parameter. Case sensitivity depends on your system (File::FNM_CASEFOLD is ignored), as does the order in which the results are returned.
http://ruby-doc.org/core-2.6.3/Dir.html#method-c-glob

It is not a bug, but it confused me while debugging the regression test. pocke/rubocop-regression-test#12

I think sorted files is better than randomized. It will be easier to debug because everyone gets the same output by RuboCop.

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Before submitting the PR make sure the following are checked:

• 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.
• Added an entry to the Changelog if the new code introduces user-observable changes. See changelog entry format.
• The PR relates to only one subject with a clear title
  and description in grammatically correct, complete sentences.
• Run bundle exec rake default. It executes all tests and RuboCop for itself, and generates the documentation.

[koic]

Looks like it makes sense to me 👍

[bbatsov]

I also like the suggested change.

[pocke]

Thank you for reviewing! I'll merge it after resolving the conflict.