Merge pull request #2079 from khingblue/fix-generate-descriptor

Fix #2071 replacing /bin/sh with bash when generates descriptor

generate_descriptor_proto.sh

@@ -1,4 +1,4 @@
-#!/bin/sh
+#!/usr/bin/env bash
 
 # Run this script to regenerate descriptor.pb.{h,cc} after the protocol
 # compiler changes.  Since these files are compiled into the protocol compiler