make all.bash finish on FreeBSD

R=dho
CC=golang-dev
https://golang.org/cl/156067
diff --git a/doc/progs/run b/doc/progs/run
index 486ef26..46de912 100755
--- a/doc/progs/run
+++ b/doc/progs/run
@@ -1,4 +1,4 @@
-#!/bin/bash
+#!/usr/bin/env bash
 # Copyright 2009 The Go Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style
 # license that can be found in the LICENSE file.