Improve dependency specified

* Clarify version of rubocop families
* Don't include rubocop families in test environments

refs:
  * kachick/ruby-ulid#154
  * kachick/times_kachick#73
  * kachick/ruby-ulid#42 (comment)

Gemfile

@@ -6,6 +6,13 @@ group :development, :test do
   gem 'rake'
 end
 
+group :development do
+  gem 'rubocop', require: false
+  gem 'rubocop-rake', require: false
+  gem 'rubocop-performance', require: false
+  gem 'rubocop-rubycw', require: false
+end
+
 group :test do
   gem 'test-unit'
   gem 'warning'

irb-power_assert.gemspec

@@ -26,9 +26,9 @@ Gem::Specification.new do |gem|
   gem.add_development_dependency 'warning', '>= 1.2.0', '< 2.0'
   gem.add_development_dependency 'rake', '>= 13.0.3', '< 20.0'
   gem.add_development_dependency 'rubocop', '>= 1.14.0', '< 1.15.0'
-  gem.add_development_dependency 'rubocop-rake'
-  gem.add_development_dependency 'rubocop-performance'
-  gem.add_development_dependency 'rubocop-rubycw'
+  gem.add_development_dependency 'rubocop-rake', '>= 0.5.1', '< 0.6.0'
+  gem.add_development_dependency 'rubocop-performance', '>= 1.11.3', '< 1.12.0'
+  gem.add_development_dependency 'rubocop-rubycw', '>= 0.1.6', '< 0.2.0'
 
   gem.required_ruby_version = '>= 2.5.0'