Change CI script hash-bang from /bin/env to /usr/bin/env

Historically, the /bin directory on Unix has a reduced set of commands used for small mounts while booting the system. As such, it is common for /bin to be missing the env command.

For the same historical reasons, /usr/bin tends to have most if not all commands provided to the user environment. Thus, /usr/bin/env is more likely to exist than /bin/env. This is in fact the case for Mac OSX, which is a very widely used version of *nix.

Thus, it is better to use #!/usr/bin/env as the hash-bang in scripts.