Widen upper dependency bounds

[fiadliel]

• aeson: < 1.5 -> < 1.6
• base64-bytestring: < 1.1 -> < 1.2
• QuickCheck: < 2.14 -> < 2.15

(tested with cabal test in nix env)

[fiadliel]

Tests also passed with latest nixpkgs-unstable, packages pinned to latest minor version, and a shell built with nix-shell -p '[ghc cabal-install zlib zlib.dev]'

Due (I think) to sol/doctest#245, I had to add write-ghc-environment-files: always to cabal.project to get doctests to compile.

[rashadg1030]

@fiadliel I see this PR has been up for a few days. I'm going to go ahead and merge this unless you want to add anymore to this PR.