Suggestion for the default robots.txt

Some Google Search Console tools are unable to load CSS files and report errors when you check a "mobile friendly" site build with Grav.

I suggest to add these two lines in the default robots.txt of Grav in order to avoid these problems:

User-agent: Googlebot
Allow: *.css$
---

Hi, you can propose an edit by making a Pull Request on https://github.com/getgrav/grav/blob/develop/robots.txt . That said, it's weird as the CSS should be allowed. In which directory is that denied CSS file located?