Incompatible with gem-based themes in safe mode

[Ben Balter]

Because the plugin sanitizes all load paths relative to the site source, gem-based themes cannot use sass in safe mode.

Steps to reproduce:

1. Create (or use an existing) theme that relies on sass
2. Require the theme in you confirm
3. Build the site in safe mode

Expected:

Theme's sass load path outside the site root is included as a load path and build succeeds with sass converted to CSS

Actual:

Build failed due to missing includes.

/cc benbalter/jekyll-remote-theme#58

[Ashwin Maroli]

Thank you for reporting this @benbalter. I've submitted a PR for review 👆