Update c3.js and c3.min.js

c3.js

@@ -5043,15 +5043,20 @@
         var minY, maxY, minX, maxX;
         var i,j, id;
 
+        var stacked;
         // detect if we have stacked group
-        var stacked = false;
-        var groups = $$.api.groups();
-        groups.forEach(function(elem){
-            if(elem.length) {
-                stacked = true;
-            }
-        });
-
+        if ($$.ed3Config.stacked) {
+            stacked = true;
+        } else {
+            stacked = false;
+            var groups = $$.api.groups();
+            groups.forEach(function (elem) {
+                if (elem.length) {
+                    stacked = true;
+                }
+            });
+        }
+        
         var stackedSum = [];
 
         var allData = $$.api.data();