Refactor BridgeDB's use of `sha` module to use `hashlib` instead.

Everytime the sha module is imported, the following DeprecationWarning occurs:

DeprecationWarning: the sha module is deprecated; use the hashlib module instead

We should probably heed its advice. Unless something strange is being done somewhere with the sha module, we should pretty much be able to do 's/sha\.sha\(/hashlib\.sha\(/'.