Update google-fonts-plugin to 3.0.0

[SirPole]

Hello! I am developer of google-fonts-plugin.

I made an error in releasing google-fonts-plugin 2.1.0, which is resolved by your plugin and does not work then. I've updated your code to match changes made to my plugin...

Since i don't work with gatsby, I didn't do any tests.

Thanks for understanding, let me know if you need anything else from me! :)

closes #8
closes #6

[kennedyrose]

Upon closer inspection, I'm not sure we can use google-fonts-plugin anymore. We need access to the function the saves the CSS files. Is this function still available in 3.0.0?

[SirPole]

I will look into it more during the weekend. My plugin is made for webpack use so I rely on webpack saving these files...

Is there any reason why you can't save the files yourself? What was wrong with the code I proposed?

[kennedyrose]

this.requestFontsCSS isn't available. I can't remember why I was relying on your plugin instead of saving the files out. It's been a while and I unfortunately haven't had the time to work on this plugin in a while.