Replaced ack by ag

I’m using ack 100 times a day, it’s written in Perl and a bit slow when grepping a big directory. I recently switched to ag (aka the_silver_searcher). It’s much faster and ignores file patterns from your .gitignore. I see no reason to use ack anymore so:

$ brew install the_silver_searcher
$ brew remove ack
$ echo "alias ack=ag" >> ~/.zshrc # my muscle memory doesn't want to switch