dev-manual, mega-manual: Updated the downloads picture.

(From yocto-docs rev: 67c71f5a51749e4f15987ce7cb3ae8f22436bb93)

Signed-off-by: Scott Rifenbark <scott.m.rifenbark@intel.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>