ChartJS - Line Chart - Y axis scale problem ?

Line Chart - Y axis scale problem ?

HTML

<script src="https://cdnjs.cloudflare.com/ajax/libs/Chart.js/2.0.0-beta/Chart.js"></script>
<div id="slider" style="width: 500px;"></div>
<canvas id="canvas" height="300" width="500"></canvas>

CSS

canvas { background-color : #eee;
}

JavaScript

var data = {
    labels: ["January", "February", "March", "April", "May", "June", "July"],
    datasets: [
        {
            label: "My First dataset",
            fill: false,
            backgroundColor: "rgba(220,220,220,0.2)",
            borderColor: "rgba(220,220,220,1)",
            borderCapStyle: 'butt',
            borderDash: [],
            borderDashOffset: 0.0,
            borderJoinStyle: 'miter',
            pointBorderColor: "rgba(220,220,220,1)",
            pointBackgroundColor: "#fff",
            pointBorderWidth: 1,
            pointHoverRadius: 5,
            pointHoverBackgroundColor: "rgba(220,220,220,1)",
            pointHoverBorderColor: "rgba(220,220,220,1)",
            pointHoverBorderWidth: 2,
            tension: 0.1,
            data: [65, 59, 80, 81, 56, 55, 40]
        },
        {
            label: "My Second dataset",
            fill: true,
            backgroundColor: "rgba(220,220,220,0.2)",
            borderColor: "rgba(220,220,220,1)",
            pointBorderColor: "rgba(220,220,220,1)",
            pointBackgroundColor: "#fff",
            pointBorderWidth: 1,
            pointHoverRadius: 5,
            pointHoverBackgroundColor: "rgba(220,220,220,1)",
            pointHoverBorderColor: "rgba(220,220,220,1)",
            pointHoverBorderWidth: 2,
            data: [28, 48, 40, 19, 86, 27, 90]
        }
    ]
};

var options = {
	responsive: false
};

Chart.helpers.extend(Chart.controllers.line.prototype, {
    fireSliderEvent: function(point, canvas, boundingRect){
    	 var mouseX = Math.round((boundingRect.left + point._view.x) / (boundingRect.right - boundingRect.left) * canvas.width / this.chart.chart.currentDevicePixelRatio);
			var mouseY = Math.round((boundingRect.top + point._view.y) / (boundingRect.bottom - boundingRect.top) * canvas.height / this.chart.chart.currentDevicePixelRatio);
       var oEvent = document.createEvent('MouseEvents');
        oEvent.initMouseEvent('click', true, true,...