Update shebang to use /usr/bin/env for portability

[SZanko]

Changed the shebang from #!/usr/bin/bash to #!/usr/bin/env bash to improve script portability across different environments where bash may not be located in /usr/bin/. This ensures compatibility on systems with alternative bash paths. e.g. nixos

[Adda0]

Hey. This is a great idea. I have been meaning to make a Nix package, and this is a nice first step.

The shebang should be #!/usr/bin/env bash, but you use #!/bin/env bash in the scripts. /bin/env is less portable for, e.g. BSD systems.