Theme check and file_put_contents

I checked my theme, i get this warnings like this
———————–
WARNING: file_put_contents was found in the file functions.php possible file operations.

Line 153: file_put_contents($css_dir.’style.css’, $css, LOCK_EX);
———————–
I used file_gut_contents and file_put_contents to get my color scheme from ini file and generate the css cache then put it in css folder.

https://github.com/parmaja/wp_metallic
https://github.com/parmaja/wp_metallic/tree/master/schemes

Is there any way to do that without any warning?

Thanks in advance
Zaher Dirkey