Warning: EPERM, rename

[TheHalcyonSavant]

Step to reproduce on Windows:
1). bower cache clean
2). grunt cdnify
Works fine, but if you continue again without clearing the cache:
3). reopen bash
4). grunt cdnify

Warning: EPERM, rename '..\AppData\Roaming\bower\cache\packages\1e5d36753a767
2512aa68fc8cdf5a6ce\1.2.18-build.233%2Bsha.e906aaf' Use --force to continue.

I suppose this is somehow related to #49 and the "-build" package suffix.