Conform to hAtom by specifying updated time of entries

I was using [Google's structured data testing tool](http://www.google.com/webmasters/tools/richsnippets) and noticed this error:

![missing_updated](https://f.cloud.github.com/assets/478311/766321/63798d58-e85c-11e2-83b3-963b30c9febe.png)

Turns out the [hAtom Entry Updated element](http://microformats.org/wiki/hatom#Entry_Updated) is required but wasn't always being included.

The existing conditional was incorrect, so `data-updated="true"` was always being included. That data attribute doesn't seem to be used, and since it wasn't being included accurately anyways I replaced it with the `class="updated"` required by hAtom.

I also removed the `pubdate` attribute from the two places it existed since [it was dropped from HTML 5](http://www.w3.org/wiki/User:Tantekelik/drop_pubdate).

After deploying these changes, I no longer see that error from Google's structured data testing tool.