declare rails version in migrations

db/migrate/20120605121861_aggregated_my_project_page_migrations.rb

@@ -20,7 +20,7 @@
 require Rails.root.join("db","migrate","migration_utils","migration_squasher").to_s
 require 'open_project/plugins/migration_mapping'
 # This migration aggregates the migrations detailed in MIGRATION_FILES
-class AggregatedMyProjectPageMigrations < ActiveRecord::Migration
+class AggregatedMyProjectPageMigrations < ActiveRecord::Migration[5.0]
 
   MIGRATION_FILES = <<-MIGRATIONS
     20110804151010_add_projects_overviews.rb

db/migrate/20130903172842_my_project_page_migrate_serialized_yaml.rb

@@ -20,7 +20,7 @@
 
 require Rails.root.join("db","migrate","migration_utils","legacy_yamler").to_s
 
-class MyProjectPageMigrateSerializedYaml < ActiveRecord::Migration
+class MyProjectPageMigrateSerializedYaml < ActiveRecord::Migration[5.0]
   include Migration::LegacyYamler
 
   def up

db/migrate/20130904181242_rename_blocks_keys.rb

@@ -18,7 +18,7 @@
 # See doc/COPYRIGHT.md for more details.
 #++
 
-class RenameBlocksKeys < ActiveRecord::Migration
+class RenameBlocksKeys < ActiveRecord::Migration[5.0]
   REPLACED = {
     "issuesassignedtome" => "work_packages_assigned_to_me",
     "issuesreportedbyme" => "work_packages_reported_by_me",