fixup comment

Author: scwhittle

sdks/python/apache_beam/options/pipeline_options.py

@@ -1023,7 +1023,8 @@ def _add_argparse_args(cls, parser):
         '--enable_streaming_engine',
         default=True,
         action='store_true',
-        help='Deprecated. All Python pipelines use Streaming Engine. ')
+        help=
+        'Deprecated. All Python pipelines on Dataflow use Streaming Engine.')
     parser.add_argument(
         '--dataflow_kms_key',
         default=None,