Upgrade to Scalaz 7.10 and all that entains

Started upgrading Mundane and hit this. There are two changes I made that I think are _wrong_ and would appreciate feedback on - I'll leave comments on the specific lines.

/cc @etorreborre @markhibberd 
Hmm. This is annoying. I hit the same problem with `BytesQuantity` in Ivory/Mundane - I haven't looked very deeply, suggestions welcome.