C: add Evan Kroske (Google CLA)

LGTM=bradfitz
R=bradfitz
CC=golang-codereviews
https://golang.org/cl/110160045

CONTRIBUTORS

@@ -211,6 +211,7 @@ Eric Roshan-Eisner <eric.d.eisner@gmail.com>
 Erik St. Martin <alakriti@gmail.com>
 Erik Westrup <erik.westrup@gmail.com>
 Esko Luontola <esko.luontola@gmail.com>
+Evan Kroske <evankroske@google.com>
 Evan Martin <evan.martin@gmail.com>
 Evan Shaw <chickencha@gmail.com>
 Ewan Chou <coocood@gmail.com>