fixes #9445: make img responsive mixin use display block, but provide option to pass custom value to it

less/scaffolding.less

@@ -73,8 +73,8 @@ img {
 }
 
 // Responsive images (ensure images don't scale beyond their parents)
-.img-responsive {
-  display: inline-block;
+.img-responsive(@display: block;) {
+  display: @display;
   max-width: 100%; // Part 1: Set a maximum relative to the parent
   height: auto; // Part 2: Scale the height according to the width, otherwise you get stretching
 }