Update epic-light.css to set a minimum height for the 'Message' text entry box

When submitting a post, the 'Message' text entry field starts off smaller than the height of one line. To help make it clear that users can write things in this box I propose setting a min-height for this field.
Merge pull request #133 from deanhewson/patch-1

Update epic-light.css to set a minimum height for the 'Message' text ent...