set default beam groups to 1

app.py

@@ -128,8 +128,8 @@ def get_parser():
     parser.add_argument(
         "--num_beam_groups",
         type=int,
-        default=2,
-        help="Number of groups to divide nbest candidates into in order to ensure diversity among different groups of beams that yield the best n results. 1 means no group beam search.",
+        default=1,
+        help="Number of groups to divide best candidates into in order to ensure diversity among different groups of beams that yield the best n results. 1 means no group beam search. (default 1)",
     )
     return parser