📌 Pin json0 dev dependency

[alecgibson]

It's best practice to specify a version when depending directly on a
repo.

[coveralls]

Coverage remained the same at 97.41% when pulling bec7e6d on pin-json0 into 8ed35d5 on master.

[ericyhwang]

Note - This is on top of a change that switches the dependency from ottypes/json0 to https://github.com/ottypes/json0:
400ec52
b1c10d6

That fixed an issue where an install on NPM 6 hanged. GitHub turned off support for unencrypted Git protocol requests, and it seems that NPM 6 defaults to those.
https://twitter.com/ruyadorno/status/1526388587918499842?s=20&t=20Pt1gZThwZ5AoKgaYHf5w
https://github.blog/2021-09-01-improving-git-protocol-security-github/