This should finally fix travis ci

Author: Byron

git/test/test_docs.py

@@ -431,7 +431,7 @@ def test_references_and_objects(self, rw_dir):
 
         # [31-test_references_and_objects]
         git = repo.git
-        git.checkout('head', b="my_new_branch")         # create a new branch
+        git.checkout('HEAD', b="my_new_branch")         # create a new branch
         git.branch('another-new-one')
         git.branch('-D', 'another-new-one')             # pass strings for full control over argument order
         git.for_each_ref()                              # '-' becomes '_' when calling it