The .cabal file lists "hashable >= 1.1 && < 1.2", and hashable is now on the incompatible version 188.8.131.52. I don't think (although I haven't tested this) updating the bounds will break anything.
Okay, I'm wrong, the new hashable doesn't export the combine function.
Replaced combine with hashWithSalt
combine isn't exported by the newest version of Data.Hashable. Goes some way to fixing issue #60