Fix discussion overlap

- Increase discussion min-height to stop overflow

Before
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![image](https://cloud.githubusercontent.com/assets/960919/4991535/f2e81cb8-698c-11e4-9d38-bfd34557ac7a.png)
After
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![image](https://cloud.githubusercontent.com/assets/960919/4991541/00354026-698d-11e4-8d5a-bd1a97679b08.png)