Reduce article image filesizes for Ojuju, Roboto Flex

[emmamarichal]

See PR #7518 where @davelab6 wrote:

@nathan-williams noted that the Ojuju image3.gif is a whopping 1.5Mb, and so I ran gifsicle to downscale and optimize it to 317kb

gifsicle --resize-width 1200 -O=3 --lossy=80 image3.gif;

gifsicle also shaved 1kb off image5.gif with no changes.

And for Roboto Flex, @felipesanches pointed out its hero.png was 17mb (LOL) so I converted it to 166kb JPG :)

sips -Z 800 -s format jpeg -s formatOptions 80 hero.png -o hero.jpg; jpegoptim hero.jpg; 

cc @davelab6 @chrissimpkins

[davelab6]

Thanks @emmamarichal :) Assigning to @yanone to complete execution of the image clean-up task using his knowledge of web development good practices :)