Remove unnecessary nesting selectors

scss/_list-group.scss

@@ -112,7 +112,7 @@
           margin-top: 0;
         }
 
-        & + .list-group-item {
+        + .list-group-item {
           border-top-width: $list-group-border-width;
           border-left-width: 0;
 

scss/mixins/_grid.scss

@@ -47,7 +47,7 @@
 // numberof columns. Supports wrapping to new lines, but does not do a Masonry
 // style grid.
 @mixin row-cols($count) {
-  & > * {
+  > * {
     flex: 0 0 auto;
     width: 100% / $count;
   }