In the absence of an opt-in to multiple specific languages in the
preferences, it makes more sense to filter by the user's presumed
language only (interface language or `lang` override)
* disable NewCops
* update TargetRubyVersion
* Fix Lint/MissingSuper for ActiveModelSerializers::Model
* Fix Lint/MissingSuper for feed
* Fix Lint/FloatComparison
* Do not use instance variables