Fix for aeson-2.0.0.0

[Former user]

aeson just released a major version bump, and jwt seems to be incompatible

[Brandon Chinn]

Hi, author of the issue here. Not sure how to create a pull request off my fork, but here are my changes:

https://bitbucket.org/brandon-leapyear/haskell-jwt/branches/compare/brandon-leapyear/haskell-jwt:chinn%2Faeson puffnfresh/haskell-jwt:master#diff

[Brian McKenna]

Thanks Brandon, I've merged that. Will do a release soon.