Update pygments.css

insert a line
```
.highlight .cm{color:#998;font-style:italic;}
```
so that haskell code will display one line comment. The color is chosen as multi-line comments.

See [this link](http://exercism.io/submissions/5244b9ac67790bd66a0001bd) for comments, and [this link](http://exercism.io/submissions/5244cab767790b5d210001d7) for effects.