remove region definition for line comment

`//` is not comment in [CSS 2.1][1] and also in [CSS3][2].

[1]: http://www.w3.org/TR/CSS21/syndata.html#comments
[2]: http://www.w3.org/TR/css3-syntax/#comments
Merge pull request #33 from hail2u/remove-line-comment-definition

remove region definition for line comment