removed deprication issue in invoice migartion, less noise for deployers

db/migrate/20150320132023_create_invoices.rb

@@ -1,7 +1,7 @@
 class CreateInvoices < ActiveRecord::Migration
   def change
     create_table :invoices do |t|
-      t.timestamps
+      t.timestamps null: false
     end
   end
 end

db/schema.rb

@@ -227,8 +227,8 @@ ActiveRecord::Schema.define(version: 20150320132023) do
   add_index "epp_sessions", ["updated_at"], name: "index_epp_sessions_on_updated_at", using: :btree
 
   create_table "invoices", force: :cascade do |t|
-    t.datetime "created_at"
-    t.datetime "updated_at"
+    t.datetime "created_at", null: false
+    t.datetime "updated_at", null: false
   end
 
   create_table "keyrelays", force: :cascade do |t|