Increase script portability

Instead of presuming that bash is installed at /bin/bash, use `$PATH`.  Official [bash docker container](https://hub.docker.com/_/bash/) installs bash at `/usr/local/bin` and recommends the use of `env`

scripts/get

-#!/bin/bash
+#!/usr/bin/env bash
 
 # Copyright 2016 The Kubernetes Authors All rights reserved.
 #