fix: force experimental decorators for danet

[ArturSharapov]

Danet relies on experimental decorators requiring experimentalDecorators to be set to true since the release of Deno 1.40, as declared in the release blog.

This PR adds deno.json containing the required option to danet and danet_v2 frameworks, fixing error and error accordingly.

An example of a successful run can be found here.