Update binder.py

I fixed `urllib.urlencode` to `urlencode` in line 135

tweepy/binder.py

@@ -132,7 +132,7 @@ def bind_api(**config):
             # Query the cache if one is available
             # and this request uses a GET method.
             if self.use_cache and self.api.cache and self.method == 'GET':
-                cache_result = self.api.cache.get('%s?%s' % (url, urllib.urlencode(self.session.params)))
+                cache_result = self.api.cache.get('%s?%s' % (url, urlencode(self.session.params)))
                 # if cache result found and not expired, return it
                 if cache_result:
                     # must restore api reference