Remove subtlepatterns hotlink

You will also need to create a gh-pages branch that contains the `groovepaper.png` file. I can't open a pull request for a branch that you haven't created (at least to my knowledge...) so you will need to add it using the following.

$ git symbolic-ref HEAD refs/heads/gh-pages
$ rm .git/index
$ git clean -fdx
$ wget http://subtlepatterns.com/patterns/groovepaper.png

Add/commit, then 

$ git push origin gh-pages