Set base constraint to >= 4.6
Set base constraint to >= 4.6

The project has only ever been built on GHC 7.6 or greater, so this
enforces that constraint. The cabal-version setting has always been
>= 1.16 so builds on earlier GHC versions fail.

See http://matrix.hackage.haskell.org/package/jose-jwt
tekul/jose-jwt