Merge pull request #3817 from gitlabhq/link_to_spinach_in_readm

link to spinach in the README. Closes #3810

README.md

@@ -117,7 +117,7 @@ Start it with [Foreman](https://github.com/ddollar/foreman)
         bundle exec rake spec
-* Spinach integration tests
+* [Spinach](https://github.com/codegram/spinach) integration tests
         bundle exec rake spinach