Fix crc buffer error

Dependency "crc" was not pinned to a major version. 
crc v 1.0 removed the buffer export that node-static-asset depended upon. 

This PR uses buffer-crc32 for buffer crc processing and pins crc to 1.x.x.

I also removed some uncalled code in hash.js in a second commit. Up to you whether to merge that as well or just take the first commit that fixes the actual problem.

Thanks
Dave