C: add Nick Cooper (Google CLA).

LGTM=dsymonds
R=dsymonds
CC=golang-codereviews, nmvc
https://golang.org/cl/169580043

CONTRIBUTORS

@@ -452,6 +452,7 @@ Nicholas Katsaros <nick@nickkatsaros.com>
 Nicholas Presta <nick@nickpresta.ca> <nick1presta@gmail.com>
 Nicholas Sullivan <nicholas.sullivan@gmail.com>
 Nicholas Waples <nwaples@gmail.com>
+Nick Cooper <nmvc@google.com>
 Nick Craig-Wood <nick@craig-wood.com> <nickcw@gmail.com>
 Nicolas Kaiser <nikai@nikai.net>
 Nicolas Owens <mischief@offblast.org>