Use compass image path

This fixes an issue where images wouldn't show up when pulling in canon via bower.

If Canon moves away from compass in the future, it would be nice to keep an images-path type of variable for this use case.
Turns out this image doesn't exist and this class is not styled out like the other status classes w/ background images (they have the padding left). Not sure how it was missed. I only noticed because when I tried updating this to image-url there was an error in my compass/sass output.