Use RAILS_VERSION on Gemfile

Gemfile

@@ -17,4 +17,11 @@ platforms :jruby do
   gem 'activerecord-jdbcsqlite3-adapter'
 end
 
-gem 'rails', '~> 4.0.0'
+version = ENV["RAILS_VERSION"] || "4.0.2"
+rails = case version
+        when "master"
+          {:github => "rails/rails"}
+        else
+          "~> #{version}"
+        end
+gem "rails", rails

Gemfile.edge

@@ -1,20 +0,0 @@
-source 'https://rubygems.org'
-
-gemspec
-
-platforms :ruby do
-  gem 'sqlite3', '1.3.8'
-end
-
-platforms :mri do
-  gem 'coveralls', require: false
-  gem 'simplecov', require: false
-end
-
-platforms :jruby do
-  gem 'activerecord-jdbcsqlite3-adapter'
-end
-
-# Use Rails master + current dependencies
-gem 'rails', github: 'rails/rails'
-gem 'arel', github: 'rails/arel'

Gemfile.rails3

@@ -1,19 +0,0 @@
-source 'https://rubygems.org'
-
-gemspec
-
-platforms :ruby do
-  gem 'sqlite3', '1.3.8'
-end
-
-platforms :mri do
-  gem 'coveralls', require: false
-  gem 'simplecov', require: false
-end
-
-platforms :jruby do
-  gem 'activerecord-jdbcsqlite3-adapter'
-end
-
-gem 'minitest', '~> 4.0'
-gem 'rails', '~> 3.2'