Merge pull request travis-ci#2469 from nodanaonlyzuul/master

Add missing word 'gem' and '.'

Author: Pezi777

user/speeding-up-the-build.md

@@ -75,7 +75,7 @@ file](https://github.com/rails/rails/blob/master/.travis.yml) for more examples.
 
 Parallelizing the test suite on one virtual machine depends on the language and test runner:
 
-- For Ruby and RSpec use the [parallel_tests](https://github.com/grosser/parallel_tests)
+- For Ruby and RSpec use the [parallel_tests](https://github.com/grosser/parallel_tests) gem.
 - For Java, use the built-in feature [to run tests in parallel
   using JUnit](http://incodewetrustinc.blogspot.com/2009/07/run-your-junit-tests-in-parallel-with.html).