add spec for #413 (#533)

spec/integration/rails_4.2.0/app/models/sub1/no_namespace.rb

+class NoNamespace < ActiveRecord::Base
+  enum foo: [:bar, :baz]
+end

spec/integration/rails_4.2.0/db/migrate/20140705000020_create_no_namespaces.rb

+class CreateUsers < ActiveRecord::Migration
+  def change
+    create_table :no_namespaces do |t|
+      t.integer :foo
+      t.timestamps
+    end
+  end
+end