Fix highlighting one line block comment(#190)

@sabof Please check this branch version.

https://github.com/defunkt/coffee-mode/blob/fix-block-comment/coffee-mode.el

### before

![block-comment0](https://f.cloud.github.com/assets/554281/1800512/ab4bddb8-6bc7-11e3-89cb-743646df01b5.png)


### after

![block-comment1](https://f.cloud.github.com/assets/554281/1800513/b06ee2ae-6bc7-11e3-9b38-2fbc9fee4965.png)