Use print() syntax in README (#681)

Since 2.7 supports this syntax as well, this will help not to confuse new people.

README.md

@@ -32,7 +32,7 @@ g = Github("access_token")
 
 # Then play with your Github objects:
 for repo in g.get_user().get_repos():
-    print repo.name
+    print(repo.name)
 ```
 
 ## Documentation