Rename CNN.jpg to cnn.jpg so CSS can find it

[hdoupe]

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[hdoupe]

I thought this was fixed in #889. It turns out git's diff functionality is case-insensitive when it comes to file names. So, this change was never displayed in the git diff and I did not double check to make sure the change was checked in. You can force git to be case-sensitive with regard to filenames via the git mv command, e.g. git mv CNN.jpg cnn.jpg. Anyways this is resolved now.