Change Work Challenge background image

As requested by UX

Bug: 27829562
Change-Id: Ib893dca102cdccf46102fa45e3501d43fd17b558
diff --git a/res/drawable-nodpi/work_challenge_background.png b/res/drawable-nodpi/work_challenge_background.png
index d38668f..50f0c76 100644
--- a/res/drawable-nodpi/work_challenge_background.png
+++ b/res/drawable-nodpi/work_challenge_background.png
Binary files differ