use color-name 1.0.0

Fix bug introduced in https://github.com/harthur/color-string/commit/426e35416c6c776443898eb60b8043e1044ebc8f
Ref https://github.com/cssnext/cssnext/issues/53
Merge pull request #14 from MoOx/patch-1

use color-name 1.0.0