JPEG output: enable progressive compression
JPEG output: enable progressive compression

I made a corresponding update in canvas that has now been merged:
https://github.com/LearnBoost/node-canvas/commit/d72c1bbf022b0c56e242211f25c584c4eb6a4e6b

Progressive JPEGs are smaller (2-7%) and have a lower time-to-first
paint in browsers.

iFixit/node-markup,iFixit/node-markup,iFixit/node-markup