text: Title: Change config file default name
  Body: Our default config path is `.scanapi.yaml`, which is not so explicit as it could.
  
  https://github.com/scanapi/scanapi/blob/master/scanapi/settings.py#L5
  
  Some other possibilities:
  
  - scanapi.conf (like [redis](https://redis.io/topics/config), or [postgresql](https://www.postgresql.org/docs/9.3/config-setting.html))
  - scanapi.init (like [pytest](https://docs.pytest.org/en/latest/customize.html))
  - .scanapi (like [rspec](https://github.com/rspec/rspec/wiki#rspec))
  
  My favorite one is the first, because in my opinion it is the most explicit. 
  
  Besides we also need to:
  - Update documentation at [scanapi/website](https://github.com/scanapi/website/tree/master/_docs_v1) 
  - Update examples at [scanapi/examples](https://github.com/scanapi/examples) 