cleanup gemspec
add rubocop
fix MethodAndVariableSnakeCase
fix Semicolon
fix AvoidFor
fix SpaceAfterControlKeyword
fix SpaceInsideHashLiteralBraces
fix CollectionMethods
fix FavorUnlessOverNegatedIf
fix Attr
fix WordArray
fix Tab
fix SpaceAroundBraces
fix Blocks
fix EmptyLines
fix RescueException
fix WhileUntilModifier
fix TrivialAccessors
fix Void
fix RedundantSelf