Update networknt/json schema validator to indicate support for 2020-12 and 2019-09

[justin-tay]

As of 1.3.1 the networknt/json-schema-validator supports 2020-12 and 2019-09.

• https://www.creekservice.org/json-schema-validation-comparison/functional#summary-results-table

[github-actions]

Hey there 👋!

Are you an implementer of a new JSON Schema related tool, or an interested user submitting a tool you like?
If so, thanks for considering adding your tool to our collection -- and if not, sorry, I'm just a bot looking at which pages you're modifying!

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In the interim, if you haven't already, there's a few things you might be interested in reviewing or confirming:

1. Short description: Tell us a small bit about your tool! We love staying up to date on what's out there, and what your intentions are in writing it.
2. Come Join Our Slack!: We have an #implementers channel for anyone interested in or building JSON Schema tooling!
   An invite can be found here or on our homepage!
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   You can find that page here in our documentation.
   Have a read through and consider whether you implement or should implement any of what's there.
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   If it makes sense for your kind of tool, consider writing a harness which connects it to Bowtie. Instructions for doing so can be found in the tutorial in Bowtie's documentation.

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Thanks a bunch for your awesome contribution!

[jdesrosiers]

Great work on the upgrades!