Loosen json dependency requirement

[aukevs]

I'm using fontcustom in a project that uses a json gem version of 2.0.0. We are using a forked version of the gem, would you like me to create a merge request for that? Or is the dependency really required?

[tarragon]

Bumping this issue. json has a security issue and the recommended upgrade path is to go to 2.3.0. There is no equivalent in 1.x, but fontcustom is locking at 1.x.

[ChristoferVinoth]

@kaizau I have solved this issue in this PR#386. Please do review this PR and assign this issue to me

[DougInAMug]

Ping @endtwist