[Fix #70] Fix a false positive for Rails/TimeZone

[koic]

Fixes #70.

This PR fixes a false positive for Rails/TimeZone when setting EnforcedStyle: strict and using Time.current.

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• Wrote good commit messages.
• Commit message starts with [Fix #issue-number] (if the related issue exists).
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• Squashed related commits together.
• Added tests.
• Added an entry to the Changelog if the new code introduces user-observable changes. See changelog entry format.
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• If this is a new cop, consider making a corresponding update to the Rails Style Guide.