change selector instantiation to be less greedy

The problem was on a results page this plugin was instantiated `n` times. This was causing `(n(n+1))/2` number of queries to Google on a results page.

A little whitespace thrashing... but the real change is 1 line LN160. Change the selector so that it is only instantiating on record view pages.

I have checked the following:
 - [ ] gallery view
 - [ ] normal view
 - [ ] brief view
 - [ ] previews 
 - [ ] browse nearby (js plugin and page)

All seem to have book covers rendering properly with this change.