Update libreoffice.rb

Version update 4.1.2 => 4.1.3
Merge pull request #1662 from alexsergeyev/patch-1

Update libreoffice.rb
Guard against unspecified casks in CLI
remove empty app dirs from caskroom on uninstall

previously an install + uninstall would leave around an empty dir with
the app's name. now we clean that up.

refs #1461
Merge pull request #1663 from phinze/1461-remove-empty-caskroom-dirs-on-uninstall

remove empty app dirs from caskroom on uninstall