Pulled in a bad version of OAS 3.1 schema

[mgabeler-lee-6rs]

The 2.1.0 release of this package (latest) pulled in a version of the OAS 3.1 schema missing an important (to me) fix: https://github.com/OAI/OpenAPI-Specification/commit/a8bd1a502a5de5050282b95cc96b6738cb0c418a

As such, it rejects all my OAS 3.1 schemas that use the proper field name for describing server template variables.

There's quite a few other fixes to the upstream schema since this repo last updated as well.