Dot in filename

[AyWa]

Bug description

Seems like . can not be use in PATH.

For example:

• '/users/{username}' is defined in a filename: users@{username}.yaml

But if we want to have users.whatever/{username} I dont know anyway to defined it correctly.
If the filename is users.whatever@{username}.yaml it will fail with:

> swagger-repo validate

Validating definition...
Failed OpenAPI3 schema validation:

undefined:
  1) #/ should be object but got undefined