grunt

dist/css/bootstrap.css

@@ -5274,7 +5274,8 @@ a.list-group-item.active > .badge,
           transition: all 0.2s ease-in-out;
 }
 
-.thumbnail > img {
+.thumbnail > img,
+.thumbnail a > img {
   display: block;
   height: auto;
   max-width: 100%;