correct sample object format in output

Author: Toby Hodges

_episodes/16-file-formats.md

@@ -48,7 +48,7 @@ Now invoke `cwl-runner` with the tool wrapper and the input object on the
 command line:
 
 ```
-$ cwltool metadata_example.cwl sample.json
+$ cwltool metadata_example.cwl sample.yml
 /usr/local/bin/cwltool 1.0.20161114152756
 Resolved 'metadata_example.cwl' to 'file:///media/large_volume/testing/cwl_tutorial2/metadata_example.cwl'
 [job metadata_example.cwl] /tmp/tmpNWyAd6$ /bin/sh \