Reference bash instead of sh

[asieira]

I've had problems in Ubuntu because the script begins with #!/bin/sh but uses bash-specific syntax. I would like to recommend that the first line is instead changed to #!/usr/bin/env bash as per https://stackoverflow.com/a/10383546/2482776.

[jason-klein]

Thank you for this script! Works great on our private AWS servers! Our Debian default shell is not bash, so we had to make same adjustment @asieira mentioned above.