chartjs.html: switch to `$.` like everywhere else (#2798)

pages/charts/chartjs.html

@@ -949,8 +949,8 @@
     //- LINE CHART -
     //--------------
     var lineChartCanvas = $('#lineChart').get(0).getContext('2d')
-    var lineChartOptions = jQuery.extend(true, {}, areaChartOptions)
-    var lineChartData = jQuery.extend(true, {}, areaChartData)
+    var lineChartOptions = $.extend(true, {}, areaChartOptions)
+    var lineChartData = $.extend(true, {}, areaChartData)
     lineChartData.datasets[0].fill = false;
     lineChartData.datasets[1].fill = false;
     lineChartOptions.datasetFill = false
@@ -1016,7 +1016,7 @@
     //- BAR CHART -
     //-------------
     var barChartCanvas = $('#barChart').get(0).getContext('2d')
-    var barChartData = jQuery.extend(true, {}, areaChartData)
+    var barChartData = $.extend(true, {}, areaChartData)
     var temp0 = areaChartData.datasets[0]
     var temp1 = areaChartData.datasets[1]
     barChartData.datasets[0] = temp1
@@ -1038,7 +1038,7 @@
     //- STACKED BAR CHART -
     //---------------------
     var stackedBarChartCanvas = $('#stackedBarChart').get(0).getContext('2d')
-    var stackedBarChartData = jQuery.extend(true, {}, barChartData)
+    var stackedBarChartData = $.extend(true, {}, barChartData)
 
     var stackedBarChartOptions = {
       responsive              : true,