docs($http): remove trailing comma

Remove trailing comma to keep the same flow with all other code examples on page.

src/ng/http.js

@@ -371,7 +371,7 @@ function $HttpProvider() {
      *  headers: {
      *    'Content-Type': undefined
      *  },
-     *  data: { test: 'test' },
+     *  data: { test: 'test' }
      * }
      *
      * $http(req).success(function(){...}).error(function(){...});