upgrade issue Yii Framework from version 2.0.15.1 to 2.0.16.1
Not sure about the Yii message, though it may be irrelevant. The Twig message refers to an issue where Twig itself was upgraded (to 2.7.2) which broke Craft. The makers of Craft were able to publish an fix within 48 hours.

Update to the latest version of Craft, this has already been fixed.