os/exec: fix typo in documentation
R=golang-dev, gri
CC=golang-dev
https://golang.org/cl/5797073
diff --git a/src/pkg/os/exec/exec.go b/src/pkg/os/exec/exec.go
index ebe92a9..bbd0490 100644
--- a/src/pkg/os/exec/exec.go
+++ b/src/pkg/os/exec/exec.go
@@ -59,7 +59,7 @@
// If either is nil, Run connects the corresponding file descriptor
// to the null device (os.DevNull).
//
- // If Stdout and Stderr are are the same writer, at most one
+ // If Stdout and Stderr are the same writer, at most one
// goroutine at a time will call Write.
Stdout io.Writer
Stderr io.Writer
