title: Unresolved reference: NavArgs after added some arguments to destination
body: <p>I'm working on a small project and trying to use the new navigation architecture components. When i'm trying to add some arguments to a destination i got "Unresolved reference: NavArgs" error.</p>
  
  <p>I followed this guide <a href="https://developer.android.com/topic/libraries/architecture/navigation/navigation-pass-data#kotlin" rel="noreferrer">https://developer.android.com/topic/libraries/architecture/navigation/navigation-pass-data#kotlin</a>
  and already added </p>
  
  <p><code>classpath "android.arch.navigation:navigation-safe-args-gradle-plugin:1.0.0-alpha11"</code> </p>
  
  <p>to my project gradle file and also added </p>
  
  <p><code>apply plugin: 'androidx.navigation.safeargs.kotlin'</code> </p>
  
  <p>to my app gradle file.</p>
  
  <p>As seen in the guide above i want to use <code>val args: AddKittenFragmentArgs by navArgs()</code> to get the passed arguments. But <code>navArgs()</code> isn't recognized.</p>
  
  <p>Also <code>NavArgs</code> in the generated code isn't resolved.</p>
  
  <pre><code>data class MyFragmentArgs(val argOne: String? = "\"\"", val argTwo: String? = "\"\"") : NavArgs
  </code></pre>