add myself to CONTRIBUTORS.md

Author: nwh

CONTRIBUTORS.md

@@ -9,6 +9,7 @@ Many thanks to the following developers for contributing to this project:
 - [Justin Charlong](https://github.com/jcharlong)
 - [Louis Sautier](https://github.com/sbraz)
 - [Martin Larralde](https://github.com/althonos)
+- [Nick Henderson](https://github.com/nwh)
 - [Will McGugan](https://github.com/willmcgugan)
 - [Zmej Serow](https://github.com/zmej-serow)
 - [Morten Engelhardt Olsen](https://github.com/xoriath)