Add myself to contributors (#3766)

First contribution was PR #3730, merged on 2 January 2017 UTC.

CONTRIBUTORS.txt

@@ -229,3 +229,4 @@ Andreas Pelme, 2016/12/13
 Mike Chen, 2016/12/20
 Alejandro Pernin, 2016/12/23
 Yuval Shalev, 2016/12/27
+Morgan Doocy, 2017/01/02