CONTRIBUTORS: add Bjorn Tipling <bjorn.tipling@gmail.com>

R=golang-dev, bradfitz
CC=golang-dev
https://golang.org/cl/5645085
diff --git a/AUTHORS b/AUTHORS
index 4ef7bd3..ec71bb9 100644
--- a/AUTHORS
+++ b/AUTHORS
@@ -32,6 +32,7 @@
 Ben Olive <sionide21@gmail.com>
 Benny Siegert <bsiegert@gmail.com>
 Berengar Lehr <berengar.lehr@gmx.de>
+Bjorn Tipling <bjorn.tipling@gmail.com>
 Blake Mizerany <blake.mizerany@gmail.com>
 Bobby Powers <bobbypowers@gmail.com>
 Caine Tighe <arctanofyourface@gmail.com>