[contributors.md] Add Stéphan Gorget to the contributor list

forgot to update it in d237c228ac4f941ad27d1723dd5a216ecf3ca2d1

contributors.md

@@ -104,3 +104,4 @@ Thank you to all contributors:
 * [paulch](https://github.com/paulch)
 * [Nathan Dautenhahn](https://github.com/ndauten)
 * [Sachin Patil](https://github.com/psachin)
+* [Stéphan Gorget](https://github.com/phantez)