C: update email address for utkarsh-extc

Change-Id: If657dab2df19d3b0c2ff9869a64e3a97446646ac
GitHub-Last-Rev: b921b01cf4e5bcbbc65fb1fb0b5cd836bda73596
GitHub-Pull-Request: golang/go#34637
Reviewed-on: https://go-review.googlesource.com/c/go/+/198041Reviewed-by: Dmitri Shuralyov <dmitshur@golang.org>

CONTRIBUTORS

@@ -777,7 +777,7 @@ GitHub User @tatsumack (4510569) <tatsu.mack@gmail.com>
 GitHub User @tell-k (26263) <ffk2005@gmail.com>
 GitHub User @uhei (2116845) <uhei@users.noreply.github.com>
 GitHub User @uropek (39370426) <uropek@gmail.com>
-GitHub User @utkarsh-extc (53217283) <53217283+utkarsh-extc@users.noreply.github.com>
+GitHub User @utkarsh-extc (53217283) <utkarsh.extc@gmail.com>
 GitHub User @yuanhh (1298735) <yuan415030@gmail.com>
 GitHub User @ZZMarquis (7624583) <zhonglingjian3821@163.com>
 Giulio Iotti <dullgiulio@gmail.com>