Drop local fork of GitPython for 2.1.8 release

2.1.8 incorporates the noted fixes.

Story: 2001393
Task: 5982
Change-Id: I828506bd7c1a1f7ce088e958361782b6cbc71f5a
diff --git a/requirements.txt b/requirements.txt
index 4b8be3c..39a2b02 100644
--- a/requirements.txt
+++ b/requirements.txt
@@ -7,11 +7,7 @@
 Paste
 WebOb>=1.2.3
 paramiko>=1.8.0,<2.0.0
-# Using a local fork of gitpython until at least these changes are in a
-# release.
-# https://github.com/gitpython-developers/GitPython/pull/682
-# https://github.com/gitpython-developers/GitPython/pull/686
-git+https://github.com/jeblair/GitPython.git@zuul#egg=GitPython
+GitPython>=2.1.8
 python-daemon>=2.0.4,<2.1.0
 extras
 statsd>=1.0.0,<3.0