Make webapp validatorUrl self-referential

[gnowland]

When deploying application behind a proxy the swagger ui shows "invalid" badge due to application attempting to validate api with validator hosted on https://validator.swagger.io, this change ensures that the swagger ui for the application uses itself to validate.

I posit this should not effect public validator-badge hosted at https://validator.swagger.io as the validator url is currently https://validator.swagger.io/validator and will remain https://validator.swagger.io/validator after this change.