macos: switch to bash-completion@2
macos: switch to bash-completion@2

This variant is designed for Bash 4.2+, which is what I'm using
everywhere.

https://github.com/scop/bash-completion

This also includes support for user-level completions under
$XDG_DATA_HOME/bash-completion (~/.local/share/bash-completion).

jparise/dotfiles,jparise/dotfiles,jparise/dotfiles,jparise/dotfiles