[FIX] product_import: use update() instead of write()

It is needed in order to have a safe recomputation of fields of other models.
There was an issue in a third-party add-on which has a field recomputed
when a new  is added to  of the product.

product_import/wizard/product_import.py

@@ -200,7 +200,7 @@ def _save_product(self, product_vals, chatter_msg):
         """Create / Update a product."""
         product = product_vals.pop("recordset", None)
         if product:
-            product.write(product_vals)
+            product.update(product_vals)
             logger.debug("Product %s updated", product.default_code)
         else:
             product_active = product_vals.pop("active")