Fix created_at

I think this is the reason why in the blog site says "Posted on May 22, 2014"

![fix typo](https://www.evernote.com/shard/s162/sh/adc41f22-899e-41ee-9046-deb0c04b8435/8693719fd362b92d95a28c23cb0ff416/deep/0/Get-your-ticket-to-one-(or-more!)-of-these-great-conferences---Rails-Girls-Summer-of-Code.png)