feat(pm)!: make fish default

Previously bash was the default shell, now it is fish! For a long while, I was disatisfied with bash. I tried zsh, but had some other problems - I've tried fish recently and been quite happy with it, so let's just switch everyone over :) BREAKING-CHANGE: Some things that were written specifically for bash might not work anymore. I haven't done an in-depth review of if any of the bash uses are important to create fish counterparts for