Drop: all vendor prefix mixins because autoprefixer

less/scaffolding.less

@@ -8,12 +8,10 @@
 // Heads up! This reset may cause conflicts with some third-party widgets.
 // For recommendations on resolving such conflicts, see
 // http://getbootstrap.com/getting-started/#third-box-sizing
-* {
-  .box-sizing(border-box);
-}
+*,
 *:before,
 *:after {
-  .box-sizing(border-box);
+  box-sizing: border-box;
 }
 
 
@@ -96,7 +94,7 @@ img {
   background-color: @thumbnail-bg;
   border: 1px solid @thumbnail-border;
   border-radius: @thumbnail-border-radius;
-  .transition(all .2s ease-in-out);
+  transition: all .2s ease-in-out;
 
   // Keep them at most 100% wide
   .img-responsive(inline-block);