title: Cannot resolve method 'formKey' in ACRA 4.7.0
body: <p>i tried setting up acra for my android project today, but it didnt work. I followed the instructions, importet the acra lib in gradle (compile 'ch.acra:acra:4.7.0')
  Then i added this:</p>
  
  <pre><code>@ReportsCrashes(formKey = "", mailTo = "mail@adress.com", mode = ReportingInteractionMode.NOTIFICATION)
  protected void onCreate(Bundle savedInstanceState) {
      super.onCreate(savedInstanceState);
      ACRA.init(this.getApplication());
  </code></pre>
  
  <p>I get the error <strong>Cannot resolve method 'formKey'</strong>, but when deleting formkey from parameters, i get <strong>@ReportsCrashes not applicable to method</strong></p>
  
  <p>I also tried</p>
  
  <pre><code>@ReportsCrashes(formUri = "http://www.yourselectedbackend.com/reportpath")
  </code></pre>
  
  <p>and </p>
  
  <pre><code>@ReportsCrashes(formKey = "", formUri = "http://www.yourselectedbackend.com/reportpath")
  </code></pre>
  
  <p>and get the same errors. Anyone knows the issue/solution? The wiki at <a href="https://github.com/ACRA/acra/wiki" rel="nofollow">https://github.com/ACRA/acra/wiki</a> seems outdated and there is no issue about this.</p>