misc/wasm: extend executable compatibility

The path /bin/bash is not available on all operating systems.
Use /usr/bin/env bash to find the system bash interpreter.

Change-Id: I493e462a8e261b7fbbd3f3c0b1d10e55c5ed783b
Reviewed-on: https://go-review.googlesource.com/c/go/+/463977
Reviewed-by: Bryan Mills <bcmills@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
Run-TryBot: Johan Brandhorst-Satzkorn <johan.brandhorst@gmail.com>
Run-TryBot: Dmitri Shuralyov <dmitshur@golang.org>
Reviewed-by: Dmitri Shuralyov <dmitshur@google.com>
Reviewed-by: Dmitri Shuralyov <dmitshur@golang.org>
Reviewed-by: Evan Phoenix <evan@phx.io>
diff --git a/misc/wasm/go_js_wasm_exec b/misc/wasm/go_js_wasm_exec
index fcbd0e4..db4d2cb 100755
--- a/misc/wasm/go_js_wasm_exec
+++ b/misc/wasm/go_js_wasm_exec
@@ -1,4 +1,4 @@
-#!/bin/bash
+#!/usr/bin/env bash
 # Copyright 2018 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.