Fix closing html tag in help/cli

This fixes the display errors currently viewable at http://exercism.io/help/how-to-access-exercises.

Before:
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![screen shot 2013-12-17 at 9 00 27 am](https://f.cloud.github.com/assets/170351/1764779/0da37368-672c-11e3-8b93-d86e93f54074.png)

After:
---
![screen shot 2013-12-17 at 9 00 47 am](https://f.cloud.github.com/assets/170351/1764782/125281ba-672c-11e3-9060-4d332929fe25.png)