Fix Lint/NonAtomicFileOperation cop error in case of implicit receiver

[viralpraxis]

echo 'mkdir(path) unless FileTest.exist?(path)' | rubocop --stdin bug.rb --only Lint/NonAtomicFileOperation -d

An error occurred while Lint/NonAtomicFileOperation cop was inspecting bug.rb:1:0.
undefined method `name' for an instance of Parser::Source::Map::Send
lib/rubocop/cop/lint/non_atomic_file_operation.rb:135:in `autocorrect_replace_method'
lib/rubocop/cop/lint/non_atomic_file_operation.rb:123:in `autocorrect'
lib/rubocop/cop/lint/non_atomic_file_operation.rb:108:in `block in register_offense'

This patch removes offenses for IO-related methods without implicit receiver.

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• The PR relates to only one subject with a clear title and description in grammatically correct, complete sentences.
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• Commit message starts with [Fix #issue-number] (if the related issue exists).
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• 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!