FB open graph does not support SVG images only use png/jpg/jpeg on guide pages
FB open graph does not support SVG images only use png/jpg/jpeg on guide pages

- Add explicit width/height and description to satisfy open graph debugger warnings
- This will fallback to the user's avatar image if the stack image isn't the
  right format.
- We're planning on transitioning to png for stack images so this should
  automatically work once that change happens.
    - Follow #89 for more discussion on that topic.

paulocheque/guides-cms,paulocheque/guides-cms,paulocheque/guides-cms,pluralsight/guides-cms,pluralsight/guides-cms,pluralsight/guides-cms