Change retweeters parameter to 'cursor'

According to the documentation
(https://dev.twitter.com/rest/reference/get/statuses/retweeters/ids)
the cursoring parameter is called 'cursor' and not 'count'.

Author: pejirout

twitter/api.py

@@ -1708,7 +1708,7 @@ def GetRetweeters(self,
         while True:
             if cursor:
                 try:
-                    parameters['count'] = int(cursor)
+                    parameters['cursor'] = int(cursor)
                 except ValueError:
                     raise TwitterError({'message': "cursor must be an integer"})
             resp = self._RequestUrl(url, 'GET', data=parameters)