Update contributors list

https://github.com/samaaron/sonic-pi/graphs/contributors?from=2013-07-28&to=2015-01-28&type=c

Author: samaaron

CONTRIBUTORS.md

@@ -28,15 +28,20 @@ grow and improve the Sonic Pi code base:
 
 * [Martin Keegan](https://github.com/mk270)
 * [Nicolas Dermine](https://github.com/nicoder)
+* [Robin Newman](https://github.com/rbnpi)
+* [Martin Zeilinger](https://github.com/st01c)
+* [G. Martin Butz](https://github.com/mbutz)
 * [Steve Traylen](https://github.com/traylenator)
 * [Bruce Adams](https://github.com/bruceadams)
-* [Ben Nuttall](https://github.com/bennuttall)
 * [Will Stephenson](https://github.com/wstephenson)
 * [Katie Miller](https://github.com/codemiller)
+* [Ben Nuttall](https://github.com/bennuttall)
 * [Daniel Canelhas](https://github.com/dcanelhas)
 * [Ruzsa Balázs](https://github.com/cellux)
 * [Karl Hiner](https://github.com/khiner)
+* [Cosmin Stroe](https://github.com/cstroe)
 * [Joseph Haig](https://github.com/jrmhaig)
 * [Graham Taylor](https://github.com/vinnievg)
-* [Robin Newman](https://github.com/rbnpi)
-* [Cosmin Stroe](https://github.com/cstroe)
+* [Nigel Michki](https://github.com/nigeil)
+* [Emlyn Corrin](https://github.com/emlyn)
+* [Alex McLean](https://github.com/yaxu)