Allow random-1.3

[andreasabel]

See:

• random-1.3.1 commercialhaskell/stackage#7648

[endgame]

Doesn't look as simple as a bound raising here: rvar is in this repo, has no upper bound, and is broken when you try to build with random == 1.3 and allow-newer:random-fu:random. rvar probably needs some revisions to add upper bounds.