fix argument order (#3637)

src/transformers/modeling_tf_transfo_xl.py

@@ -488,7 +488,7 @@ class TFTransfoXLMainLayer(tf.keras.layers.Layer):
         else:
             return None
 
-    def _update_mems(self, hids, mems, qlen, mlen):
+    def _update_mems(self, hids, mems, mlen, qlen):
         # does not deal with None
         if mems is None:
             return None