Fix .jpg to .png reference for broken image
Fix .jpg to .png reference for broken image

I shrank the image in a previous commit but forgot to update the extension.
codecombat/codecombat,javatlacati/codecombat,javatlacati/codecombat,codecombat/codecombat,javatlacati/codecombat,codecombat/codecombat,javatlacati/codecombat,javatlacati/codecombat,codecombat/codecombat,codecombat/codecombat