fix Function1Comonad#cojoin
Make glorified Foldable `identity`s into actual `identity`s.
Merge pull request #385 from xuwei-k/Function1Comonad-cojoin

fix Function1Comonad#cojoin
Merge pull request #386 from S11001001/topic/foldable-identities

Make glorified Foldable `identity`s into actual `identity`s.