Vendor files

Check that the versions of the following files match the current vendor versions:

1. _includes/vendor/anchor_headings.html: https://github.com/allejo/jekyll-anchor-headings

2. _layouts/vendor/compress.html: https://github.com/penibelst/jekyll-compress-html

3. _sass/vendor/normalize.scss/normalize.scss: https://github.com/necolas/normalize.css

4. assets/js/vendor/lunr.min.js: https://github.com/olivernn/lunr.js