Use line_with_comment? instead of bad API

[ydah]

RuboCop::Cop::Util#comment_line? is flagged by rubocop/rubocop#8405 as a bad API. So I propose to fix not use this method.

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Before submitting the PR make sure the following are checked:

• Feature branch is up-to-date with master (if not - rebase it).
• Squashed related commits together.
• [-] Added tests.
• [-] Updated documentation.
• [-] Added an entry to the CHANGELOG.md if the new code introduces user-observable changes.
• The build (bundle exec rake) passes (be sure to run this locally, since it may produce updated documentation that you will need to commit).

[bquorning]

Do you know if processed_source.line_with_comment? is available only in recent versions of rubocop / rubocop_ast?

[ydah]

This method was added in rubocop-ast 0.2.0, so it seems to have been around since the beginning.

• Fix ProcessedSource#commented? for multi-line ranges. Add ProcessedSource#commented_line? rubocop-ast#55
• https://github.com/rubocop/rubocop-ast/blob/master/CHANGELOG.md#020-2020-07-19