9.10 support

[michaelpj]

Not sure what needs to happen here, but at least updating to use a new ghc-lib-parser.

[jhrcek]

Here's a PR making it compile with 9.10, all tests passing with cabal (check CI in my fork: jhrcek#1). The only thing that seems to be missing is stackage snapshot with 9.10 support so we can upgrade stylish-haskell's stack CI..