Library does not build with aeson > 2

[jgm]

This library needs updating in light of the API changes in aeson 2.0.1.0.
See haskell/aeson#881 for a migration guide.

[chris-martin]

Revisions to existing releases on Hackage to add an upper bound would be appreciated.

[ysangkok]

@chris-martin I have performed the revisions as requested.

To anyone interested in Aeson 2 compatibility, I'd ask you to review my PR #63! I was thinking that I'd release it when it is reviewed, as Thomas has granted me maintainership. please test the released version and report bugs on https://github.com/ysangkok/aeson-diff.