Fix bottom padding on comment item

Before
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![before](https://f.cloud.github.com/assets/74132/1513197/9b94f9aa-4add-11e3-8f26-2b11d346db81.jpg)

After
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![after](https://f.cloud.github.com/assets/74132/1513198/9ddc2e40-4add-11e3-9559-c7e33bcf098b.jpg)