docs($httpBackend): Grammar correction - Add a "s" 

Add a "s" to the word "control" to change it to "controls" in lines 1408, 1422, 1436, 1453, 1470, 1487, 1500 to follow proper grammatical rules.  Same exact correction to the same exact sentence and word for all lines listed above.  Important change to ensure the documentation follows proper grammatical rules.  Also changes these lines to match the same sentence used earlier in the doc on line 1236.

Before: "Returns an object with `respond` method that control how a matched request is handled."

After: "Returns an object with `respond` method that controls how a matched request is handled."