Fix axis.labels api

c3.js

@@ -4240,7 +4240,7 @@
         return isString(option) ? option : option ? option.text : null;
     };
     Axis.prototype.setLabelText = function setLabelText(axisId, text) {
-        var $$ = this, config = $$.config,
+        var $$ = this.owner, config = $$.config,
             option = this.getLabelOptionByAxisId(axisId);
         if (isString(option)) {
             if (axisId === 'y') {

spec/api.axis-spec.js

@@ -0,0 +1,54 @@
+describe('c3 api axis', function () {
+    'use strict';
+
+    var chart, args;
+
+    beforeEach(function (done) {
+        chart = window.initChart(chart, args, done);
+    });
+
+    describe('axis.labels', function () {
+
+        it('should update args', function () {
+            args = {
+                data: {
+                    columns: [
+                        ['data1', 30, 200, 100],
+                        ['data2', 50, 20, 10]
+                    ],
+                    axes: {
+                        data1: 'y',
+                        data2: 'y2'
+                    }
+                },
+                axis: {
+                    y: {
+                        label: 'Y Axis Label'
+                    },
+                    y2: {
+                        show: true,
+                        label: 'Y2 Axis Label'
+                    }
+                }
+            };
+            expect(true).toBeTruthy();
+        });
+
+        it('should update y axis label', function () {
+            chart.axis.labels({y: 'New Y Axis Label'});
+            var label = d3.select('.c3-axis-y-label');
+            expect(label.text()).toBe('New Y Axis Label');
+            expect(label.attr('dx')).toBe('-0.5em');
+            expect(label.attr('dy')).toBe('1.2em');
+        });
+
+        it('should update y axis label', function () {
+            chart.axis.labels({y2: 'New Y2 Axis Label'});
+            var label = d3.select('.c3-axis-y2-label');
+            expect(label.text()).toBe('New Y2 Axis Label');
+            expect(label.attr('dx')).toBe('-0.5em');
+            expect(label.attr('dy')).toBe('-0.5em');
+        });
+
+    });
+});

src/axis.js

@@ -134,7 +134,7 @@ Axis.prototype.getLabelText = function getLabelText(axisId) {
     return isString(option) ? option : option ? option.text : null;
 };
 Axis.prototype.setLabelText = function setLabelText(axisId, text) {
-    var $$ = this, config = $$.config,
+    var $$ = this.owner, config = $$.config,
         option = this.getLabelOptionByAxisId(axisId);
     if (isString(option)) {
         if (axisId === 'y') {