fix: remove margin in case of the value of col is a breakpoint

Author: thingsym

sass/_flexbox-grid-mixins.scss

@@ -169,9 +169,7 @@ $flexbox-grid-mixins-box-sizing: border-box !default;
 		@if $flexbox-grid-mixins-grid-type == skeleton {
 				@include grid-col-margin($margin: 0 $gutter / 2 $gutter);
 		} @else if $flexbox-grid-mixins-grid-type == margin-offset {
-			@if type-of($col) == string and $col == 'breakpoint' {
-				@include grid-col-margin($margin-right: 0);
-			} @else if type-of($last-child) == bool and $last-child == true {
+			@if type-of($last-child) == bool and $last-child == true {
 				@include grid-col-margin($margin-right: 0);
 			} @else {
 				@include grid-col-margin($margin-right: $gutter);