Calculate Accurate Shipping Cost

The shipping cost wasn't accurate when a shipment contained multiple packages as only the prices from the different packages were compiled, while the cost remained the one returned for a first package.

Author: nicolasddev

app/code/Magento/Shipping/Model/Rate/PackageResult.php

@@ -68,6 +68,7 @@ public function getAllRates()
                             throw new \InvalidArgumentException('Same object received from carrier.');
                         }
                         $rate->setPrice($rate->getPrice() + $currentRate->getPrice());
+                        $rate->setCost($rate->getCost() + $currentRate->getCost());
                         continue 2;
                     }
                 }