Update JSON section

[hyrodium]

With the release of JSON.jl v1.0, JSON3.jl is now deprecated.

https://juliaio.github.io/JSON.jl/stable/migrate/#Migration-guides
https://github.com/quinnj/JSON3.jl

[KronosTheLate]

That is incredible! That is exactly what I am generally hoping for when a new and better package with a number-suffix comes along. Should definitively be reflected on the site indeed.

[tp2750]

Thank you for the heads up @hyrodium .
Please comment on the PR if you like: #147