How to minify the css of a specific folder on Gulp?

Question

gulp.js

there is this hierarchy:

-site_1
--src_css
--- reset.css
--- index.css
--css
---main.min.css

-site_2
--src_css
--- reset.css
--- index.css
--css
---main.min.css

The sources for each site are in /src_css/*, the minified version is in /css/main.min.css.
It is necessary when changing css files, css was going to be used for a specific site, the rest should not be touched

Answer 1

This is a node conflict with dependencies.
Remove node_modules and reinstall dependencies