return result from callback

returning the result of the callback allows you to chain the promise
like you would expect

test/specs/helpers/spread.spec.js

@@ -9,5 +9,13 @@ describe('helpers::spread', function () {
 
     expect(value).toEqual(50);
   });
+
+  it('should return callback result', function () {
+    var value = spread(function (a, b) {
+      return a * b;
+    })([5, 10]);
+
+    expect(value).toEqual(50);
+  });
 });