Compress empty folders about grunt-contrib-compress

[ctalkington]

this comes down to the fact that most grunt plugins work at the file level, not folder, and its currently not supported by archiver, the underlying lib.

I may consider adding a helper to archiver which would make this possible but it would still need some work on the task side to detect folder, make sure its empty, and then call special helper. Otherwise, you would have a crap load of pointless folder entries in your zip file, increasing file size.