Adds border bottom to active h2 link

The `h2` link is missing it's border-bottom to match with `h3` and `h4`.

Before:
![h2 before](https://dl.dropboxusercontent.com/u/25783709/H2-before.png)

After:
![h2 after](https://dl.dropboxusercontent.com/u/25783709/H2-after.png)

Also removes some trailing white space – to match the rest of the file.