Make gen_jit_dispatch runnable (pytorch#12018)

Summary:
Pull Request resolved: pytorch#12018

Tried to use the file and ran into a small bug, this fixes it

Differential Revision: D10013231

fbshipit-source-id: 4cf8c29cf9e2cedd7a28fa0cc0196e5144a54bf2

Author: bwasti

tools/jit/gen_jit_dispatch.py

@@ -351,7 +351,7 @@ def main():
                         help='path to Declarations.yaml')
     parser.add_argument('out', metavar='OUT',
                         help='path to output directory')
-    parser.add_argument('template-path', metavar='TEMPLATE_PATH',
+    parser.add_argument('template_path', metavar='TEMPLATE_PATH',
                         help='path to templates directory')
     args = parser.parse_args()
     gen_jit_dispatch(args.declarations, args.out, args.template_path)