progrium/dokku — pull request #573 by eriknomitch (2014-05-12 20:30:52+00:00)
Title: Use command instead of which for apt-get existential check in bootstrap.sh

`command` is a better way to check if a command exists than `which`. See [this StackOverflow post](http://stackoverflow.com/questions/592620/how-to-check-if-a-program-exists-from-a-bash-script).