Upgrade to httplib2 version 0.7.7.

Reviewed in https://codereview.appspot.com/6849064/.
diff --git a/setup_oauth2client.py b/setup_oauth2client.py
index b0cdf9b..b02348b 100644
--- a/setup_oauth2client.py
+++ b/setup_oauth2client.py
@@ -24,7 +24,7 @@
 ]
 
 install_requires = [
-    'httplib2>=0.7.6',
+    'httplib2>=0.7.7',
     'python-gflags',
     ]