dev-manual: Updated title .PNG file

The manual title has changed to "Yocto Project Development Tasks
Manual".

(From yocto-docs rev: aa6b7959df1725257ee598f828d3e99e595308e5)

Signed-off-by: Scott Rifenbark <srifenbark@gmail.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>