Add tests for og:updated_time in open_graph helper, and add ability to turn it off

[matthew-andrews]

I think I might be one of very few people who have ever tried to do this…

I deploy my static site from CircleCI to S3 automatically (the tool I used to actually push the files to S3 compares the MD5 hashes of the locally generated files against those in AWS and skips any that haven't change) when I push to master because on each build the og:updated_time changes it re-uploads each article.

I've worked around this by now after discovering if you set the updated option of the open_graph helper to be a string that removes the og:updated_time meta tag…… But this feels like a bit of a hack.

It would be nice if you could just do:-

open_graph({
  twitter_id: config.twitter,
  google_plus: config.google_plus,
  updated: false
});

So that's what this pull requests adds support for. Also I notice the og:updated_time feature didn't have any tests, so I added a couple.

Thanks.

Matt