After updating to serverless v4 I ran into an issue where the generated schema was always empty.

We are using serverless-compose, so we have a folder structure like this:

services/
  service-1/
    serverless.yml
  service-2/
    serverless.yml
serverless-compose.yml

It seems that the schema files are paths relative to the service directory, but the cwd is the root folder, thus none of the schema files can be found.

This PR should fix that problem and also resolve #648.