Make python 2.7 friendly

Author: David Walker

xbee/tornado/base.py

@@ -101,7 +101,7 @@ def process_frames(self):
     @gen.coroutine
     def wait_read_frame(self):
         frame = yield self._get_frame()
-        return self._split_response(frame.data)
+        raise gen.Return(self._split_response(frame.data))
 
     def _get_frame(self):
         future = Future()