Here is the error(s) I received after trying to run a migration:
Rails aborted! StandardError: An error has occurred, this and all later migrations canceled: Directly inheriting from ActiveRecord::Migration is not supported. Please specify the Rails release the migration was written for:
By adding the rails version number in brackets after class name the migration runs perfectly.
class acts_as_follower < ActiveRecord::Migration[5.1]
...More to come.