Update credits to include 3rd party libraries used

misaochan · web-flow · commit 5f273c9c6d1b · 2017-05-12T18:08:57.000+08:00
Including MapBox
diff --git a/CREDITS b/CREDITS
@@ -19,3 +19,9 @@ their contribution to the product.
 * Veyndan Stuart
 * Vivek Maskara
 * Neslihan Turan
+
+3rd party open source libraries used:
+* Butterknife
+* GSON
+* Timber
+* MapBox
