Fix typo

Fix typo `with-[x]co`l to `with-[x]col` in Descendants comment.

Author: KOREAN139

_assets/stylesheets/layouts/_grid.scss

@@ -53,7 +53,7 @@
 // Descendants
 // =============================================================================
 
-// Creates a grid cell. Add `with-[x]co`l to define the number of coloms the
+// Creates a grid cell. Add `with-[x]col` to define the number of coloms the
 // cell needs to span. Do not use 'with-[x]col` if you wish to span the entire
 // width.