Add support for new JSON 1.0 release

[quinnj]

No description provided.

[quinnj]

I think the failures here are unrelated? Something about checking pip interop?

[lgoettgens]

It would be great to get this in. We converted our packages to JSON 1.0 (it unfortunately was not possible to allow 0.21 at the same time), and now we are unable to use the dev version of the package inside Jupyter notebooks.

@ViralBShah @stevengj, from the commit history, it looks as if you two are mostly maintaining this. Would it be possible if one of you has a look at this? Thanks!

[hhaensel]

just filed a PR in IJulia JuliaLang/IJulia.jl#1197 that works with JSON v1 as soon as Conda's json compat is bumped to include 1

[quinnj]

Maybe @ViralBShah or @stevengj could help take a look here? I think the JSON usage/changes here are pretty minor/easy, but it seems like something else is goign wrong w/ the tests. If no one else can take a look, I can try to dig in since this package is blocking a lot of others from upgrading to JSON 1.0.