Use file name instead of 'variables' as DEFAULT_SECTION

[mickeyvip]

Currently if there are no comments in the SASS/SCSS files for sections, each section gets DEFAULT_SECTION as section name, which is set to variables.

It would be nice to use a file name as the section fallback name.

Thank you! This tool came very handy in my project to import SASS/SCSS variables into TailwindCSS config.