Update swagger-editor to 3.1+

[jrbasso]

The current version (2.10.5) doesn't work with the new Swagger 3.0 specification. The newest version of the editor supports it and brings more fields that we can use on development.

[zoellner]

I've run into the same issue. Wanted to do a PR first but ended up starting a new extension from scratch.
https://github.com/zoellner/openapi-preview
https://marketplace.visualstudio.com/items?itemName=zoellner.openapi-preview
Main differences:

• Uses built in webview panel instead of external browser (no need to run a node process on a hard coded port)
• Supports OpenAPI@3
• has swagger-ui as dependency instead of code added to repo which should make for a much easier update process

It's my first VS extension. Feedback and PRs welcome

Thanks mimarec for the inspiration