Change "/bin/bash" to "/usr/bin/env bash" in shell files (#129)

build.sh

@@ -1,4 +1,4 @@
-#!/bin/bash
+#!/usr/bin/env bash
 
 basedir=$(cd $(dirname "$0"); pwd)
 

setup.sh

@@ -1,4 +1,4 @@
-#!/bin/bash
+#!/usr/bin/env bash
 
 set -e
 

upload.sh

@@ -1,4 +1,4 @@
-#!/bin/bash
+#!/usr/bin/env bash
 
 source $(dirname "$0")/setup.sh