better demo data

demo-angularIO/src/app/areachart-demo/areachart-demo.component.ts

@@ -128,7 +128,7 @@ function randomLineData(): Array<LineChartData> {
             }
             dp.data = {
                 x: lcdp.points.length,
-                y: lcdp.points.length
+                y: last
             };
 
             lcdp.points.push( dp );