Fix warning

Author: Nicolas Rodriguez

test/dummy/db/migrate/20140729162110_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 :name

test/dummy/db/migrate/20140729162246_create_emails.rb

@@ -1,4 +1,4 @@
-class CreateEmails < ActiveRecord::Migration
+class CreateEmails < ActiveRecord::Migration[4.2]
   def change
     create_table :emails do |t|
       t.string :address

test/dummy/db/migrate/20140729162335_create_profiles.rb

@@ -1,4 +1,4 @@
-class CreateProfiles < ActiveRecord::Migration
+class CreateProfiles < ActiveRecord::Migration[4.2]
   def change
     create_table :profiles do |t|
       t.string :twitter_name

test/dummy/db/migrate/20140729164623_create_songs.rb

@@ -1,4 +1,4 @@
-class CreateSongs < ActiveRecord::Migration
+class CreateSongs < ActiveRecord::Migration[4.2]
   def change
     create_table :songs do |t|
       t.string :title

test/dummy/db/migrate/20140729164653_create_artists.rb

@@ -1,4 +1,4 @@
-class CreateArtists < ActiveRecord::Migration
+class CreateArtists < ActiveRecord::Migration[4.2]
   def change
     create_table :artists do |t|
       t.string :name

test/dummy/db/migrate/20140729164713_create_producers.rb

@@ -1,4 +1,4 @@
-class CreateProducers < ActiveRecord::Migration
+class CreateProducers < ActiveRecord::Migration[4.2]
   def change
     create_table :producers do |t|
       t.string :name

test/dummy/db/migrate/20140729165425_create_conferences.rb

@@ -1,4 +1,4 @@
-class CreateConferences < ActiveRecord::Migration
+class CreateConferences < ActiveRecord::Migration[4.2]
   def change
     create_table :conferences do |t|
       t.string :name

test/dummy/db/migrate/20140729165445_create_speakers.rb

@@ -1,4 +1,4 @@
-class CreateSpeakers < ActiveRecord::Migration
+class CreateSpeakers < ActiveRecord::Migration[4.2]
   def change
     create_table :speakers do |t|
       t.string :name

test/dummy/db/migrate/20140729165506_create_presentations.rb

@@ -1,4 +1,4 @@
-class CreatePresentations < ActiveRecord::Migration
+class CreatePresentations < ActiveRecord::Migration[4.2]
   def change
     create_table :presentations do |t|
       t.string :topic

test/dummy/db/migrate/20140729170014_create_surveys.rb

@@ -1,4 +1,4 @@
-class CreateSurveys < ActiveRecord::Migration
+class CreateSurveys < ActiveRecord::Migration[4.2]
   def change
     create_table :surveys do |t|
       t.string :name