Update description of $httpBackend.respond(...)

For the novice, the previous description was not helpful. I hope this is more so.
The line length might be an issue indeed. 

As for contractions, I find that contractions often hurt the novice more than they annoy the expert. A novice is already struggling with typos and word usage. Saddling them with contractions then further burdens the process of learning by avoiding relatively cheap opportunities for clarification and correction. In fact, there have been times I've read the documentation just to figure out what the contractions mean or to erase doubts.