toolchain: wrapper.sh: use /bin/sh instead of bash

No bash features are actually used here.

Signed-off-by: Rosen Penev <rosenp@gmail.com>
[slightly adjust commit title]
Signed-off-by: Adrian Schmutzler <freifunk@adrianschmutzler.de>

target/toolchain/files/wrapper.sh

@@ -1,4 +1,4 @@
-#!/bin/bash
+#!/bin/sh
 
 # 2009 (C) Copyright Industrie Dial Face S.p.A.
 #          Luigi 'Comio' Mantellini <luigi.mantellini@idf-hit.com>