(bug): Imagick fix

https://fix-imagick-upgrade-migration-563.minds.io/newsfeed/subscriptions

Had to fix the issues I was having locally with Imagick to enable progress on other tasks that were reliant on this. With the help of @brianhatchet I have identified that the version installed is Imagick 3.4.0. Since Imagick 3.2.0 flattenImages() has been depreciated, I have replaced this with its recommended counterpart in the attached MR