title: String resource not accessable in manifest during building process
body: <p>To avoid my API keys from getting committed on source control (git) I have made an XML resource file called <code>api_keys.xml</code> under the <code>values</code> directory. This file is listed under <code>.gitignore</code>.</p>
  
  <p>I access these string resources the usual way by using <code>@string/..</code> or <code>.getString(R.string...)</code>. This approach works everywhere but in the <code>manifest.xml</code> file. </p>
  
  <p>I have fabric set-up and in the <code>manifest</code> file this is how I try to pass the key - </p>
  
  <pre><code>&lt;meta-data
   android:name="io.fabric.ApiKey"
   android:value="@string/FABRIC_API_KEY" /&gt;
  </code></pre>
  
  <p>But, when I try to build the APK I get the following error -</p>
  
  <blockquote>
    <p>Error:Execution failed for task ':app:fabricGenerateResourcesDebug'.
    Crashlytics Developer Tools error.</p>
  </blockquote>
  
  <p>This error goes away if I replace <code>@string/FABRIC_API_KEY</code> with the actual key. </p>
  
  <p>Is there a way I can fix this? Or any other approach I can use to prevent my API keys form getting published on the source control.  </p>