Update c3.js and c3.min.js

c3.js

@@ -4418,6 +4418,14 @@
     c3_chart_internal_fn.clearLegendItemTextBoxCache = function () {
         legendItemTextBox = {};
     };
+
+    c3_chart_internal_fn.legendText = function (id){
+        var $$ = this;
+        return isDefined($$.config.data_names[id]) ?
+               $$.config.data_names[id] :
+               isDefined($$.config.data_names.id) ? $$.config.data_names.id : id; 
+    };
+
     c3_chart_internal_fn.updateLegend = function (targetIds, options, transitions) {
         var $$ = this, config = $$.config;
         var xForLegend, xForLegendText, xForLegendRect, yForLegend, yForLegendText, yForLegendRect;
@@ -4435,10 +4443,6 @@
         
         $$.clearLegendItemTextBoxCache();
 
-        function legendText(id){
-            return isDefined(config.data_names[id]) ? config.data_names[id] : isDefined(config.data_names.id) ? config.data_names.id : id; 
-        }
-
         function getTextBox(textElement, id) {
             if (!legendItemTextBox[id]) {
                 legendItemTextBox[id] = $$.getTextRect(textElement.textContent, '.c3-legend-item');
@@ -4575,7 +4579,7 @@
                 }
             });
         l.append('text')
-            .text(legendText)
+            .text($$.legendText.bind($$))
             .each(function (id, i) { updatePositions(this, id, i); })
             .style("pointer-events", "none")
             .attr('x', $$.isLegendRight || $$.isLegendInset ? xForLegendText : -200)
@@ -4604,7 +4608,7 @@
 
         texts = $$.legend.selectAll('text')
             .data(targetIds)
-            .text(legendText) // MEMO: needed for update
+            .text($$.legendText.bind($$)) // MEMO: needed for update
             .each(function (id, i) { updatePositions(this, id, i); });
         (withTransition ? texts.transition() : texts)
             .attr('x', xForLegendText)