Bump RuboCop Performance to 1.2.0

RuboCop Performance 1.2.0 has been released.
https://rubygems.org/gems/rubocop-performance/versions/1.2.0

This version includes the following fix false negative to
`Performance/RegexpMatch` cop.
rubocop/rubocop-performance#47

Gemfile

@@ -8,7 +8,7 @@ gem 'bump', require: false
 gem 'pry'
 gem 'rake', '~> 12.0'
 gem 'rspec', '~> 3.7'
-gem 'rubocop-performance', '~> 1.1.0'
+gem 'rubocop-performance', '~> 1.2.0'
 gem 'rubocop-rspec', '~> 1.32.0'
 gem 'simplecov', '~> 0.10'
 gem 'test-queue'