Upgrading Instructions for Yii Framework v2===========================================!!!IMPORTANT!!!The following upgrading instructions are cumulative. That is,if you want to upgrade from version A to version C and there isversion B between A and C, you need to following the instructionsfor both A and B.Upgrade from Yii 2.0.0----------------------* MongoDB PHP extension min version raised up to 1.4.0. You should upgrade your environment in case you are using older version.