go/test/chan1.go: fix typo

Found by Lucio De Re

R=golang-dev, gri
CC=golang-dev
https://golang.org/cl/5694071

test/ken/chan1.go

@@ -4,7 +4,7 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
-// Test communication with multiple simultanous goroutines.
+// Test communication with multiple simultaneous goroutines.
 
 package main