fix: use portable shebangs

[jamestrew]

Problem
On some systems (eg NixOS), bash is not in /bin/bash so running any of these bash scripts fail.

Solution
Use #!/usr/bin/env bash over #!/bin/bash.
Usage of #!/usr/bin/env is already prevelant in many of the skill scripts in this repo.

[heyitsnoah]

Thanks for the submission! Looks good.