Why both extension='scss' and extension='module.scss' not worked?

I did try this options and that not worked but nowhere is it written why.

```
module.file_ext=.scss
module.file_ext=.scss.module
module.name_mapper.extension='scss' -> '/SCSSModule.js.flow'
module.name_mapper.extension='module.scss' -> '/SCSSModule.js.flow'
```

I spent a lot of time to understand that what's unnecessary above

I guessed to the working version:
```
module.file_ext=.scss.module
module.name_mapper.extension='module.scss' -> '/SCSSModule.js.flow'
```