Add resources directory to gitignore

[jt-nti]

The directory is currently required since Netlify doesn't support the extended version of Hugo but we should get rid of it as soon as possible because it's a horrible work around!

Blocked by netlify/build-image#182

[jt-nti]

Should now be possible with the new build image selection setting in Netlify (currently in beta) to select the Ubuntu Xenial 16.04 image, which supports all Hugo versions.

https://www.netlify.com/docs/build-gotchas/#hugo