C: add Andres Erbsen (Google CLA)

LGTM=bradfitz, minux
R=bradfitz, minux
CC=golang-codereviews
https://golang.org/cl/119540043

CONTRIBUTORS

@@ -66,6 +66,7 @@ Amrut Joshi <amrut.joshi@gmail.com>
 Andrea Spadaccini <spadaccio@google.com>
 Andreas Jellinghaus <andreas@ionisiert.de> <anj@google.com>
 Andrei Vieru <euvieru@gmail.com>
+Andres Erbsen <andreser@google.com>
 Andrew Balholm <andybalholm@gmail.com>
 Andrew Bonventre <andybons@chromium.org>
 Andrew Bursavich <abursavich@gmail.com>