Fix @gray-light in docs

docs/_includes/css/less.html

@@ -28,7 +28,7 @@
 @gray-darker:  lighten(#000, 13.5%); // #222
 @gray-dark:    lighten(#000, 20%);   // #333
 @gray:         lighten(#000, 33.5%); // #555
-@gray-light:   lighten(#000, 60%);   // #999
+@gray-light:   lighten(#000, 46.7%); // #777
 @gray-lighter: lighten(#000, 93.5%); // #eee
 {% endhighlight %}