{{ project_root_url }} dead links on Github page

[augbog]

There are some dead links on the googlechrome.github.io/sw-toolbox homepage including the expressive approach link and the usage and api link at the bottom of the homepage.

I notice that they are using Jekyll's {{ project_root_url }} so not sure if this is jekyll specific but right now they 404.

[robdodson]

I also noticed the recipe link https://googlechrome.github.io/recipes/cache-expiration-options/ is a 404