Fix tests for GitPython>0.3.2.RC1

Catches the GitCommandError exception when a ref does
not exist.

Change-Id: I9fe2e95d64eaf06537723957c6e7eaaf9282ccab
diff --git a/requirements.txt b/requirements.txt
index dd947d6..4c85447 100644
--- a/requirements.txt
+++ b/requirements.txt
@@ -5,7 +5,7 @@
 Paste
 WebOb>=1.2.3,<1.3
 paramiko>=1.8.0
-GitPython==0.3.2.RC1
+GitPython>=0.3.2.1
 lockfile>=0.8
 ordereddict
 python-daemon