Update CREDITS to credit the Android Wikipedia app

Deskana · Deskana · commit e1a7007f6073 · 2017-05-28T09:55:08.000+01:00
We reused a code sample from the Android Wikipedia app, and will likely use more. It seems fitting to credit them.
diff --git a/CREDITS b/CREDITS
@@ -25,3 +25,6 @@ their contribution to the product.
 * GSON
 * Timber
 * MapBox
+
+3rd party open source apps from which significant code has been reused:
+* Android Wikipedia app https://github.com/wikimedia/apps-android-wikipedia
