Zero base on value axis

HTML

<script type="text/javascript" src="http://www.amcharts.com/lib/3/amcharts.js"></script>
<script type="text/javascript" src="http://www.amcharts.com/lib/3/exporting/amexport_combined.js"></script>
<script type="text/javascript" src="http://www.amcharts.com/lib/3/serial.js"></script>
<div id="chartdiv"></div>

CSS

#chartdiv {
	width	: 100%;
	height	: 500px;
}

JavaScript

var chart;

            var chartData = [{
                "country": "USA",
                    "visits": 4025,
                    "color": "#FF0F00"
            }, {
                "country": "China",
                    "visits": 1882,
                    "color": "#FF6600"
            }, {
                "country": "Japan",
                    "visits": 1809,
                    "color": "#FF9E01"
            }];


            var chart = AmCharts.makeChart("chartdiv", {
				"theme": "none",
                type: "serial",
                dataProvider: chartData,
                categoryField: "country",
                depth3D: 20,
                angle: 30,
                
                categoryAxis: {
                    labelRotation: 90,
                    gridPosition: "start"
                },

                valueAxes: [{
                    title: "Visitors",                 
                    minimum: 0
                }],

                graphs: [{

                    valueField: "visits",
                    colorField: "color",
                    type: "column",
                    lineAlpha: 0.1,
                    fillAlphas: 1
                }],

                chartCursor: {
                    cursorAlpha: 0,
                    zoomable: false,
                    categoryBalloonEnabled: false
                },
                pathToImages:"http://www.amcharts.com/lib/3/images/",
                amExport:{
                 top:21,
                  right:20,
                  exportJPG:true,
                  exportPNG:true,
                  exportSVG:true
                }
            });