title: Can't install and use "draper" gem
body: <p>I have some problems handling draper gem.</p>
  
  <ol>
  <li><p>install draper
      gem 'draper'</p>
  
  <pre><code>$ bundle install
  </code></pre></li>
  </ol>
  
  <p>and this was successful.</p>
  
  <ol start="2">
  <li><p>did <code>rails generate draper:install</code></p>
  
  <pre><code>$ rails generate draper:install
  </code></pre></li>
  </ol>
  
  <p>but I got some errors</p>
  
  <pre><code>    Expected string default value for '--test-framework'; got false (boolean)
      Expected string default value for '--helper'; got true (boolean)
      Expected string default value for '--assets'; got true (boolean)
      Expected string default value for '--test-framework'; got false (boolean)
      Expected string default value for '--helper'; got true (boolean)
      Expected string default value for '--decorator'; got true (boolean)
      Expected string default value for '--decorator'; got true (boolean)
      Expected string default value for '--jbuilder'; got true (boolean)
      Could not find generator draper:install.
  </code></pre>
  
  <ol start="3">
  <li><p>never mind, I did <code>rails generate decorator Service</code></p>
  
  <pre><code>Expected string default value for '--test-framework'; got false (boolean)
  Expected string default value for '--helper'; got true (boolean)
  Expected string default value for '--assets'; got true (boolean)
  Expected string default value for '--test-framework'; got false (boolean)
  Expected string default value for '--helper'; got true (boolean)
  Expected string default value for '--decorator'; got true (boolean)
  Expected string default value for '--decorator'; got true (boolean)
  Expected string default value for '--jbuilder'; got true (boolean)
  Expected string default value for '--test-framework'; got false (boolean)
        create  app/decorators/service_decorator.rb
  </code></pre></li>
  </ol>
  
  <p>this was successful.</p>
  
  <ol start="4">
  <li><p>made method in services_decorator</p>
  
  <pre><code>class ServiceDecorator &lt; Draper::Decorator
    delegate_all
  
    def hello
      'hello'
    end
  end
  </code></pre></li>
  <li><p>call this method from view</p>
  
  <pre><code>&lt;%= Service.first.decorate.hello %&gt;
  </code></pre></li>
  </ol>
  
  <p>but this was error,</p>
  
  <pre><code>    Could not infer a decorator for ActiveRecord::Base.
  </code></pre>
  
  <p>Can someone teach me what was wrong and how to solve this problem?
  The rails version is 4.1.7, and draper version is 2.1.0</p>