docs: fix README

Author: thingsym

README.md

@@ -168,7 +168,7 @@ Small patches and bug reports can be submitted a issue tracker in Github. Forkin
 
 * Version 0.1.5
   * update package.json
-  * add optional arguments $shorthand
+  * add optional arguments $shorthand to @mixin grid-col
 * Version 0.1.4
   * update example
   * update document