corrected CSS on new comic html to close an open div tag.
The average score appears to work, but I cannot get the test for it working yet.
Test added for comic book model.  Tests the average score.
Added average score to comic book show page. Corrected the average score attribute for the comic book to account for instances when the number of reviews/ratings is zero.
Removed extra line in the comic book average score method.
Merge pull request #27 from LaunchAcademy/add_comic_average_rating

Add comic average rating