Update c3.js and c3.min.js

c3.js

@@ -3726,6 +3726,8 @@
 
         var data = [];
         
+        data.noNegative = true;
+
         targets.forEach(function(target){
             data.push($$.cloneTarget(target));
         });
@@ -3733,7 +3735,12 @@
         for(var k = 0; k < targets[0].values.length; k++) {
             var tt = 0;
             for(c in targets) {
-                tt = tt + targets[c].values[k].value;
+                if(targets[c].values[k]){
+                    if(targets[c].values[k].value < 0){
+                        data.noNegative = false;
+                    }
+                    tt = tt + Math.abs(targets[c].values[k].value);
+                }
             }
             tr[k] = tt;
         }
@@ -5044,9 +5051,11 @@
         // if we don't need to tune
         if($$.config.normalized){
             $$.data.targets = $$.normalize($$.data._targets);
+            if($$.data.targets.noNegative){
                 $$.cachedRedraw();
                 return;
             }
+        }
             
         var apply = function(){