Make `brewdler` output more `bundler`-like

Hey @andrew, great little utility... it's definitely scratching one of my itches!  :smiley:

This pull request makes the output generated by `brewdle` more like the output generated by `bundle`, especially w.r.t. the version numbers of the formulae.

So for brew formulae that are already installed:

    Using ack (1.96)

And for brew formulae that are missing:

    Installing tree (1.6.0)

So you get something like this:

```shell
$ brewdle install 
Using ack (1.96)
Using tree (1.6.0)
Using ttyrec (1.0.8)
Using mongodb (2.2.2-x86_64)
All dependencies installed
$ brew remove tree
Uninstalling /usr/local/Cellar/tree/1.6.0...
$ brewdle install 
Using ack (1.96)
Installing tree (1.6.0)
==> ...
Using ttyrec (1.0.8)
Using mongodb (2.2.2-x86_64)
All dependencies installed
$ brewdle install
Using ack (1.96)
Using tree (1.6.0)
Using ttyrec (1.0.8)
Using mongodb (2.2.2-x86_64)
All dependencies installed
$ _
```

Thanks for your consideration!