Update Chrome Webstore Screenshots

[coliff]

not really a big deal or anything but the screenshots on the Chrome Webstore are of a very old version of the Lighthouse extension... would be nice to have updated ones so folks can see how great it looks now. :-)

[wardpeet]

i'm assigning @paulirish, maybe this is something @kusler can do too

[brendankenny]

we eventually get around to these things :)

Screenshots are updated: https://chrome.google.com/webstore/detail/lighthouse/blipmdconlkpinefehnmjammfjpmpbjk