Fix article meta continer when no byline is present

This fixes the meta container layout when no byline is present.

- Min-height sizing at mobile
- Remove double border at desktop

Thank you @kaelig for reporting.

### Before
![screenshot from 2014-03-05 09 53 02](https://f.cloud.github.com/assets/80089/2331630/76a91b94-a44c-11e3-933a-deceb40ab48c.png)
![screenshot from 2014-03-05 09 53 13](https://f.cloud.github.com/assets/80089/2331631/782410aa-a44c-11e3-96a8-d003c5bd03ee.png)

### After
![screenshot from 2014-03-05 09 53 21](https://f.cloud.github.com/assets/80089/2331633/7c6e39a6-a44c-11e3-8be6-970fd7404a9f.png)
![screenshot from 2014-03-05 09 53 34](https://f.cloud.github.com/assets/80089/2331634/7e1db006-a44c-11e3-835f-7ce78c82a4ad.png)