use url-prefix instead of regexp

[Crystal-RainSlide]

For https://github.com/overdodactyl/Stylus-Dark/blob/4e387002442b06efb39c77f67b56b2886c4e1f53/stylus-dark.user.css#L12 https://github.com/overdodactyl/Stylus-Dark/blob/4e387002442b06efb39c77f67b56b2886c4e1f53/stylus-dark.user.css#L13

regexp("chrome-extension://.*"),
regexp("moz-extension://.*")

can be replaced by:

url-prefix("chrome-extension://"),
url-prefix("moz-extension://")

Or:

regexp("(?:chrome|moz)-extension:\/\/.+")