Version path segment is not added to compiled CSS URLs

It appears as though compiled CSS is not including the version path segment in ember-cli-addon-docs deployments that use versioned docs. See https://github.com/Addepar/ember-table/issues/593 for an example.

The ember-table demo there is referring to an SVG in CSS that is failing to load with a 404. This is because the file is deployed to the version directory at `/ember-table/latest/@addepar/style-toolbox/assets/images/checkmark.svg` while the CSS is pointing to `/ember-table/@addepar/style-toolbox/assets/images/checkmark.svg`. The compiled CSS is missing the `/latest/` segment of the URL path.