Adding missing form-control class to make result consistent with tutorial screenshot

In the codelab, we have the following screenshot for the inital div
![image](https://f.cloud.github.com/assets/1711792/2236370/0b217464-9b5c-11e3-9606-b78ff36fee4e.png)

And we expect it to be rendered as the following:
![image](https://f.cloud.github.com/assets/1711792/2236375/31b567b6-9b5c-11e3-8e60-d32e89ed228e.png)

However in reality, it renders as:
![image](https://f.cloud.github.com/assets/1711792/2236377/44434db2-9b5c-11e3-9df6-788f4f72a63a.png)

It's just a simple matter of adding the 'form-control' class as per commit (also keeps it consistent with the screenshot that follows that section)