Merge pull request heroku#514 from heroku/schneems/ruby-version-mismatch

Schneems/ruby version mismatch

Author: schneems

lib/language_pack/ruby.rb

@@ -652,12 +652,20 @@ def build_bundler
           error_message = "Failed to install gems via Bundler."
           puts "Bundler Output: #{bundler_output}"
           if bundler_output.match(/An error occurred while installing sqlite3/)
-            error_message += <<ERROR
+            error_message += <<-ERROR
 
-
-Detected sqlite3 gem which is not supported on Heroku.
+Detected sqlite3 gem which is not supported on Heroku:
 https://devcenter.heroku.com/articles/sqlite3
-ERROR
+            ERROR
+          end
+
+          if bundler_output.match(/but your Gemfile specified/)
+            error_message += <<-ERROR
+
+Detected a mismatch between your Ruby version installed and
+Ruby version specified in Gemfile or Gemfile.lock:
+https://devcenter.heroku.com/articles/ruby-versions#your-ruby-version-is-x-but-your-gemfile-specified-y
+            ERROR
           end
 
           error error_message