Gemfile in active_admin_datetimepicker-0.2.0 vs Gemfile in active_admin_datetimepicker-0.3.0

@@ -1,11 +1,12 @@
 source 'https://rubygems.org'
 
 # Specify your gem's dependencies in active_admin_datetimepicker.gemspec
 gemspec
 group :test do
+  default_rails_version = '4.2.6'
   gem 'sprockets-rails', '2.3.3'
-  gem 'rails',  '4.2.0'
+  gem 'rails', "#{ENV['RAILS'] || default_rails_version}"
   gem 'rspec-rails'
   gem 'activeadmin', github: 'activeadmin'  , ref: 'd787029e5523be2eb2ed99816eb0cecca2b72862'
   gem 'coveralls', require: false # Test coverage website. Go to https://coveralls.io
   gem 'sass-rails'
   gem 'sqlite3'