Merge pull request #1581 from nextcloud/suppressInnerClassesWarnings

suppress annoying "warning: Ignoring InnerClasses"

proguard.cfg

@@ -34,3 +34,5 @@
 -keep class * implements android.os.Parcelable {
   public static final android.os.Parcelable$Creator *;
 }
+
+-keepattributes InnerClasses