Images not resolving in early static events.

[chriscoffee]

This should fix #662

I noticed that https://www.devopsdays.org/events/2016-minneapolis/speakers/ had broken images. I looked into it, and it appears that we don't have images loading correctly in archived events that have been built for the live site. If I check locally, it still doesn't work because www.devopsdays.org is baked into the static files. If I look directly at the URL of a speaker image locally (not a link to it), it does still exist and redirect to where it lives in /static: http://localhost:1313/events/2016-minneapolis/speakers/aj-bowen.jpg

Looks like the gulp task which copied old images from /public/events/2016-minneapolis/speakers/ wasn't copying them across to /dist/events/2016/minneapolis/speakers/ causing the images to be broken.

I spun up an example of the 'fixed' example of this here: https://mystifying-goodall-173afa.netlify.com/events/2016-minneapolis/speakers/aj-bowen.jpg using the same problematic image.

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This change is 

[bridgetkromhout]

Thanks, Chris! I know @mattstratton is planning a release soon - likely this is something he'll want to consider getting in!

[mattstratton]

I'll merge this in - we have to "manually" make this change into devopsdays-web since the gulp stuff is part of the repo and not part of the theme, but I think I can copy-paste it just fine :)