Update transcribe_async.py to have long GCS flac example [(#904)](GoogleCloudPlatform/python-docs-samples#904)

Author: danaharon

samples/snippets/transcribe_async.py

@@ -19,7 +19,7 @@
 
 Example usage:
     python transcribe_async.py resources/audio.raw
-    python transcribe_async.py gs://cloud-samples-tests/speech/brooklyn.flac
+    python transcribe_async.py gs://cloud-samples-tests/speech/vr.flac
 """
 
 import argparse