Added update method to the image api

Author: thevikas

src/BigCommerce/Api/Catalog/Products/ProductImagesApi.php

@@ -42,4 +42,9 @@ public function create(ProductImage $productImage): ProductImageResponse
     {
         return new ProductImageResponse($this->createResource($productImage));
     }
+
+    public function update(ProductImage $productImage): ProductImageResponse
+    {
+        return new ProductImageResponse($this->updateResource($productImage));
+    }
 }