Replace `in Rails 4` with `in Rails %version%` in deprecation message

railties/lib/rails/app_rails_loader.rb

@@ -1,4 +1,5 @@
 require 'pathname'
+require 'rails/version'
 
 module Rails
   module AppRailsLoader
@@ -9,7 +10,7 @@ module Rails
     BUNDLER_WARNING = <<EOS
 Looks like your app's ./bin/rails is a stub that was generated by Bundler.
 
-In Rails 4, your app's bin/ directory contains executables that are versioned
+In Rails #{Rails::VERSION::MAJOR}, your app's bin/ directory contains executables that are versioned
 like any other source code, rather than stubs that are generated on demand.
 
 Here's how to upgrade: