A+C: add Michael Stapelberg (individual CLA)

R=golang-dev, bradfitz
CC=golang-dev
https://golang.org/cl/6325058
diff --git a/AUTHORS b/AUTHORS
index f713032..71432b5 100644
--- a/AUTHORS
+++ b/AUTHORS
@@ -150,6 +150,7 @@
 Michael Gehring <mg@ebfe.org>
 Michael Hoisie <hoisie@gmail.com>
 Michael Lewis <mikelikespie@gmail.com>
+Michael Stapelberg <michael@stapelberg.de>
 MichaƂ Derkacz <ziutek@lnet.pl>
 Miek Gieben <miek@miek.nl>
 Mikael Tillenius <mikti42@gmail.com>