facebook/hhvm — pull request #2915 by sstewartgallus (2014-06-11 20:40:40+00:00)
Title: Declare Bash dependency in shebang

BASH_SOURCE is obviously Bash specific and so the shebang should tell
the system to use Bash.

Also while I was there I used env to get the Bash in the user's PATH
instead of just the system's Bash.