Docs: Fix filenames to match references in the docs - second time

This is just like the fix that Remington Steed sent in on Sept 4th.

These images were creating errors for me when I try to create
an epub version of the docs because they are all referenced as .jpg
but the filenames were .JPG.

Signed-off-by: Josh Stompro <github@stompro.org>
Signed-off-by: Yamil Suarez <yamil@yamil.com>