Invalid .editorconfig file should give an error instead of being ignored

Steps to reproduce:
1. Place this .editorconfig locally:
```
[*.fs]
indent_size=2,
max_line_length=80,
```
2. Run fantomas

Current results
.editorconfig file is ignored (it shouldn't have commas)

Expected results:
It should give an error, so that the user can know he has a config file with a bad format.