gs_fetch_binpkg: add proper types to args

BUG=None
TEST=precq is happy

Change-Id: I988182d35b76e109770dbc2fbbe27e620d4d093c
Reviewed-on: https://chromium-review.googlesource.com/315570
Commit-Ready: Mike Frysinger <vapier@chromium.org>
Tested-by: Mike Frysinger <vapier@chromium.org>
Reviewed-by: Filipe Brandenburger <filbranden@chromium.org>
Reviewed-by: Don Garrett <dgarrett@chromium.org>
diff --git a/scripts/gs_fetch_binpkg.py b/scripts/gs_fetch_binpkg.py
index a6c02be..a4a5ef1 100644
--- a/scripts/gs_fetch_binpkg.py
+++ b/scripts/gs_fetch_binpkg.py
@@ -27,8 +27,10 @@
   """Creates the argparse parser."""
   parser = commandline.ArgumentParser(description=__doc__)
   parser.add_argument('--boto', type='path', help='Path to boto auth file.')
-  parser.add_argument('uri', help='Google Storage URI to download')
-  parser.add_argument('filename', help='Location to store the file.')
+  parser.add_argument('uri', type='gs_path',
+                      help='Google Storage URI to download')
+  parser.add_argument('filename', type='path',
+                      help='Location to store the file.')
   return parser