Fixed a deprecation warning pointed out by admp on GitHub.

Author: joestump

oauth2/__init__.py

@@ -692,7 +692,7 @@ def sign(self, request, consumer, token):
 
         # HMAC object.
         try:
-            import hashlib.sha1 as sha # 2.5
+            from hashlib import sha1 as sha
         except ImportError:
             import sha # Deprecated