Raise bound: QuickCheck

[JackKelly-Bellroy]

Tested with:

• cabal test --constraint 'QuickCheck ^>=2.16'.
• cabal test --constraint 'QuickCheck ^>=2.17' --allow-newer=aeson:QuickCheck

Could we please have a metadata revision also?

Fixes #112

[ysangkok]

Now QuickCheck 2.17 is released, so it probably would make sense to raise the bound to include that version too.

[JackKelly-Bellroy]

We can propose a bound-raising here, but we can't solve without allow-newer because aeson won't raise bounds just yet: haskell/aeson#1147 (comment)

Since tests passed with cabal test --constraint 'QuickCheck ^>=2.17' --allow-newer=aeson:QuickCheck, I have rebased and updated this commit.