Same issue with the broken icon here too. All other docker icons, and other Sonarr releases display fine.
If I go into edit, the icon url (https://cloud.githubusercontent.com/assets/1121837/12184949/2dcc376a-b590-11e5-9a78-54b7dc5d3647.png) is correct and works fine when copy and pasted into a browser. Strangely, if I edit the url to something else - either one from someone elses build which displays on theirs, or one found on google it still shows a broken image.
Like others have said, only a minor issue but odd that all of your other apps display fine.
Many thanks for all the Docker releases, really appreciate them.