Quantify the `a` in the `Functor (Either a)` instance
Attempting to compile DH.Prelude
with Agda 2.6.1.2 yields the following
error:
$ agda DH/Prelude.agda
Checking DH.Prelude (/home/ryanglscott/Documents/Hacking/Agda/dependent/agda/DH/Prelude.agda).
Unsolved metas at the following locations:
/home/ryanglscott/Documents/Hacking/Agda/dependent/agda/DH/Prelude.agda:451,35-36
I'm unclear if this is a leftover from development or just a newer version of Agda being stricter about quantification, but either way, the fix is simple.