[Fix #53] Fix a false positive for Rails/SaveBang

[koic]

Fixes #53.

This PR fixes a false positive for Rails/SaveBang when implicitly return using finder method and creation method connected by ||.

And this PR updates .rubocop_todo.yml with rubocop --auto_gen_config to prevent the following offense.

% rubocop lib/rubocop/cop/rails/save_bang.rb
Inspecting 1 file
C

Offenses:

lib/rubocop/cop/rails/save_bang.rb:100:7: C: Metrics/ClassLength: Class
has too many lines. [164/159]
      class SaveBang < Cop ...
            ^^^^^^^^^^^^^^^^^^^^

1 file inspected, 1 offense detected

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