Add Rob to contributors file (#1090)

Author: microbit-matt-hillsdon

CONTRIBUTORS.md

@@ -2,5 +2,6 @@ Thank you to everybody that has contributed to the Python editor project:
 
 - Dania Suheimat (dania.suheimat@arm.com)
 - Matt Hillsdon (matt.hillsdon@microbit.org)
+- Robert Knight (robert@microbit.org)
 
 This version of the Python editor benefits from the great work of [the contributors](https://github.com/bbcmicrobit/PythonEditor/graphs/contributors) to [the original Python editor](https://github.com/bbcmicrobit/PythonEditor/) for the BBC micro:bit. Thanks for all your efforts!