Update avatar-stack.scss

- Fixed pointer to the anchor element

Author: JoshBowdenConcepts

src/avatars/avatar-stack.scss

@@ -119,7 +119,7 @@
       margin-left: 3px;
     }
 
-    &:not(:last-child) {
+    .avatar:not(:last-child) {
       border-left: 0;
     }
   }