Update Homebrew install instructions.

As package go into official homebrew repository.

README.md

@@ -12,7 +12,7 @@ version of git and at least Python 2.7 installed.
 
 With [Homebrew](http://brew.sh/):
 
-    brew install pr0d1r2/contrib/gitup && brew link gitup
+    brew install gitup && brew link gitup
 
 ## From source