Address issue with nested controllers

`myrails controller --name admin/articles` generates code like:

let(:admin/articles) {[]}
let(:admin/article) {create :admin/article}

describe 'GET index' do
    before do
      3.times {admin/articles << create(:admin/article)}
      get :index
    end

    it 'sets @admin/articles' do
      expect(assigns[:admin/articles]).to eq admin/articles
    end
  end