Don't let .DS_Store files break script/bootstrap

Fixes boxen/our-boxen#512

In particular, I have seen problems with the following hidden files that Mac creates:
- `.DS_Store`
- `.!59508!.DS_Store`
- `.!59554!.DS_Store`
Merge pull request #555 from idris/patch-1

Don't let .DS_Store files break script/bootstrap