do not hardcode the path to bash by using the #!/usr/bin/env bash shebang

on non-linux systems bash is not the default shell (by default) and
lives in a completely different path

Change-Id: I6580c776dda1b60b3d5c5f5f1ce4d6694ac45fe9
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/tools/depot_tools/+/1605902Reviewed-by: Robbie Iannucci <iannucci@chromium.org>
Commit-Queue: Robbie Iannucci <iannucci@chromium.org>

bb

-#!/bin/bash
+#!/usr/bin/env bash
 
 # Copyright 2019 The Chromium Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be

cipd

-#!/bin/bash -e
+#!/usr/bin/env bash
 
 # Copyright (c) 2016 The Chromium Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be

led

-#!/bin/bash
+#!/usr/bin/env bash
 
 # Copyright 2017 The Chromium Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be

luci-auth

-#!/bin/bash
+#!/usr/bin/env bash
 
 # Copyright 2018 The Chromium Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be

lucicfg

-#!/bin/bash
+#!/usr/bin/env bash
 
 # Copyright 2019 The Chromium Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be

mac_toolchain

-#!/bin/bash
+#!/usr/bin/env bash
 
 # Copyright 2017 The Chromium Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be

prpc

-#!/bin/bash
+#!/usr/bin/env bash
 
 # Copyright 2018 The Chromium Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be

vpython

-#!/bin/bash
+#!/usr/bin/env bash
 
 # Copyright 2018 The Chromium Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be