Fixes broken links to posts from archive.html

I was navigating via your archives and came across some broken links.  I believe this should fix things, but haven't tested them.

PS.  Do you manually move items from master to gh-pages or do you use a deploy script?  I started using one [with this site](https://github.com/openhatch/oh-contribution-stories/blob/master/deploy.sh) and it's so much easier.  (The content there is more complicated than what you'd need, since the site uses a couple frameworks/tools.)  Let me know if you'd like me to help you set that up.  :)