Fix extension to yml

Included sample is already `yml`

Author: manabuishii

_episodes/16-file-formats.md

@@ -39,7 +39,7 @@ checking in working examples of parameter files for your tool. This allows
 others to quickly work with your tool, starting from a "known good"
 parameterization.
 
-*sample.json*
+*sample.yml*
 
 ~~~
 {% include cwl/sample.yml %}