Specify migrations version (fixing tests)

test/dummy/db/migrate/20150713101607_create_users.rb

@@ -1,4 +1,4 @@
-class CreateUsers < ActiveRecord::Migration
+class CreateUsers < ActiveRecord::Migration[4.2]
   def change
     create_table :users do |t|
       t.string :email, unique: true, null: false

test/dummy/db/migrate/20160519075733_create_admins.rb

@@ -1,4 +1,4 @@
-class CreateAdmins < ActiveRecord::Migration
+class CreateAdmins < ActiveRecord::Migration[4.2]
   def change
     create_table :admins do |t|
       t.string :email

test/dummy/db/migrate/20160522051816_create_vendors.rb

@@ -1,4 +1,4 @@
-class CreateVendors < ActiveRecord::Migration
+class CreateVendors < ActiveRecord::Migration[4.2]
   def change
     create_table :vendors do |t|
       t.string :email

test/dummy/db/migrate/20160522181712_create_composite_name_entities.rb

@@ -1,4 +1,4 @@
-class CreateCompositeNameEntities < ActiveRecord::Migration
+class CreateCompositeNameEntities < ActiveRecord::Migration[4.2]
   def change
     create_table :composite_name_entities do |t|
       t.string :email

test/dummy/db/migrate/20161127203222_create_v1_users.rb

@@ -1,4 +1,4 @@
-class CreateV1Users < ActiveRecord::Migration
+class CreateV1Users < ActiveRecord::Migration[4.2]
   def change
     create_table :v1_users do |t|