Update c3.js and c3.min.js

c3.js

@@ -5046,7 +5046,7 @@
         var stacked;
         // detect if we have stacked group
         if ($$.ed3Config.stacked !== undefined) {
-            stacked = true;
+            stacked = $$.ed3Config.stacked;
         } else {
             stacked = false;
             var groups = $$.api.groups();