script/nuke failed to delete receipts

Can't use a bare system call because we need globbing
Merge pull request #85 from boztek/nuke-delete-receipts

Fix script/nuke to properly delete receipts
Merge branch 'master' of https://github.com/boxen/our-boxen

* 'master' of https://github.com/boxen/our-boxen:
  script/nuke failed to delete receipts