Make `brewdler` output more `bundler`-like

For brew formulae that are installed:

    Using ack (1.96)

For brew formulae that are missing:

    Installing tree (1.6.0)
Use Enumerable#find_all instead of #each

This simplifies the Ruby code a wee bit, as we don't have
to create & build up the array of dependencies ourselves!
Merge pull request #5 from pvdb/replace_each_with_find_all

Use Enumerable#find_all instead of #each
Merge pull request #4 from pvdb/bundler_like_output

Make `brewdler` output more `bundler`-like
Version 0.3.0