Fix hard-coded path to /bin/bash -> /usr/bin/env bash

On Posix systems, the path /bin/bash is not guaranteed to
exist and it is more portable to use /usr/bin/env instead.

Fixing this for yosys-config with is the most important for
a functioning installation.

Signed-off-by: Henner Zeller <h.zeller@acm.org>

misc/yosys-config.in

@@ -1,4 +1,4 @@
-#!/bin/bash
+#!/usr/bin/env bash
 
 help() {
 	{