Cabal revisions of rvar-0.2.0.3

Hackage metadata revisions edit the .cabal file after upload; each diff below is one revision.

 name:                   rvar version:                0.2.0.3+x-revision:             1 stability:              stable  cabal-version:          >= 1.6   else     build-depends:      mtl == 1.1.*   -  build-depends:        base            >= 3 && <5,+  -- MonadFailProposal breaks, fail is not member of Monad since base-4.13+  build-depends:        base            >= 3 && <4.13,                         MonadPrompt     == 1.0.*,                         random-source   == 0.3.*,                         transformers    >= 0.2 && < 0.6