Cap GitPython at 2.1.1 due to performance degradation

It appears newer versions of GitPython have slowed considerably.
Cap GitPython until https://github.com/gitpython-developers/GitPython/issues/605
is resolved.

Change-Id: Ie6c8722e8b607bb50e77fbad59e18363616f7e0d
Signed-off-by: Paul Belanger <pabelanger@redhat.com>
diff --git a/requirements.txt b/requirements.txt
index 84d84be..186e7f6 100644
--- a/requirements.txt
+++ b/requirements.txt
@@ -4,7 +4,7 @@
 Paste
 WebOb>=1.2.3
 paramiko>=1.8.0,<2.0.0
-GitPython>=0.3.3
+GitPython>=0.3.3,<2.1.2
 ordereddict
 python-daemon>=2.0.4,<2.1.0
 extras