Use 5.2 version of ActiveRecord::Migration for Active Storage

activestorage/db/migrate/20170806125915_create_active_storage_tables.rb

@@ -1,4 +1,4 @@
-class CreateActiveStorageTables < ActiveRecord::Migration[5.1]
+class CreateActiveStorageTables < ActiveRecord::Migration[5.2]
   def change
     create_table :active_storage_blobs do |t|
       t.string   :key,        null: false

activestorage/test/database/create_users_migration.rb

@@ -1,6 +1,6 @@
 # frozen_string_literal: true
 
-class ActiveStorageCreateUsers < ActiveRecord::Migration[5.1]
+class ActiveStorageCreateUsers < ActiveRecord::Migration[5.2]
   def change
     create_table :users do |t|
       t.string :name