Revise repa to allow QuickCheck 2.12

[Dan Burton]

QuickCheck 2.12.* has been released. Can the constraints on repa be relaxed accordingly?

See also: http://hackage.haskell.org/package/QuickCheck-2.12.6.1/changelog

I have verified that it builds locally like so:

stack unpack repa-3.4.1.4 && cd repa-3.4.1.4

edit stack.yaml # add the following stack.yaml
edit repa.cabal # relax the constraint on QuickCheck

stack build --test --bench --no-run-benchmarks --fast

# stack.yaml

resolver: nightly-2018-10-22

extra-deps:

- QuickCheck-2.12.6.1