New visualization for brew deps --tree

I suppose it would break parsers, but for me it's easier to visualize the deps tree with this new style.
```
$brew deps mapnik --tree
mapnik
|- pkg-config
|- libtool
|- libtiff
|- proj
|- icu4c
|- jpeg
|- boost
|- gdal
|  |- jpeg
|  |- giflib
|  |- libtiff
|  |- libgeotiff
|  |  |- libtiff
|  |  |- lzlib
|  |  |- jpeg
|  |  |- proj
|  |- proj
|  |- geos
|  |- sqlite
|  |  |- readline
|  |- freexl
|  |- libspatialite
|  |  |- proj
|  |  |- geos
|  |  |- sqlite
|  |  |  |- readline
|  |  |- freexl
|- geos
|- cairo
|  |- pixman
|  |  |- pkg-config
|  |- pkg-config
|  |- xz
|  |- glib
|  |  |- pkg-config
|  |  |- xz
|  |  |- gettext
|  |  |- libffi
```