title: Why do I get error on flurry when trying to compile to release on Android?
body: <p>when I tried to compile to release using <code>./gradlew assembleRelease
  </code>, I got these error. I didn't signed it yet, but according to <a href="http://developer.android.com/tools/building/building-cmdline.html" rel="nofollow">http://developer.android.com/tools/building/building-cmdline.html</a>, I can signed it later.</p>
  
  <pre><code>Warning: com.flurry.sdk.hn: can't find referenced class com.google.android.gms.ads.identifier.AdvertisingIdClient
  Warning: com.flurry.sdk.hn: can't find referenced class com.google.android.gms.ads.identifier.AdvertisingIdClient$Info
  Warning: com.flurry.sdk.hn: can't find referenced class com.google.android.gms.ads.identifier.AdvertisingIdClient
  Warning: com.flurry.sdk.hn: can't find referenced class com.google.android.gms.ads.identifier.AdvertisingIdClient$Info
  Warning: com.flurry.sdk.hn: can't find referenced class com.google.android.gms.ads.identifier.AdvertisingIdClient$Info
  Warning: com.flurry.sdk.hn: can't find referenced class com.google.android.gms.ads.identifier.AdvertisingIdClient$Info
  Warning: com.flurry.sdk.hn: can't find referenced class com.google.android.gms.ads.identifier.AdvertisingIdClient$Info
  Warning: com.flurry.sdk.kg: can't find referenced class com.flurry.sdk.i
  </code></pre>