[Fix #12] Allow passing boolean literals to touch

[eugeneius]

Fixes #12.

The Rails/SkipsModelValidations cop currently incorrectly registers an offense for the touch method from Shoulda Matchers' associations DSL:

it { is_expected.to belong_to(:user).touch(true) }

Active Record's touch method accepts attribute names, so we can treat touch calls that pass boolean literal arguments as false positives.

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[koic]

Thank you!