init: create the boxen tapsdir root directory.
init: create the boxen tapsdir root directory.

Otherwise the boxen tap directory may fail to be created.

RallySoftware/boxen-homebrew,RallySoftware/boxen-homebrew,n0ts/puppet-homebrew,RallySoftware/boxen-homebrew,boxen/puppet-homebrew,boxen/puppet-homebrew,n0ts/puppet-homebrew,halyard/puppet-homebrew,boxen/puppet-homebrew,n0ts/puppet-homebrew