Fixing _PaxHeader_ error on berks upload

```
E, [2014-10-09T17:07:36.832664 #19439] ERROR -- : Cookbook file attributes/PaxHeader/groups.rb has a ruby syntax error:
E, [2014-10-09T17:07:36.832905 #19439] ERROR -- : ~/.berkshelf/cookbooks/zap-0.6.0/attributes/PaxHeader/groups.rb:1: syntax error, unexpected tIDENTIFIER, expecting end-of-input
```
Minitar creates PaxHeader directories while installing (unpacking) the cookbooks into the berkshelf cache.
This will remove those directories when they are created