动态线图数据更新bug

### Version
4.5.0

### Steps to reproduce
var base = new Date(2014, 9, 3);
var oneDay = 24 * 3600 * 1000;
var date = [];

var data = [Math.random() * 150];
var now = new Date(base);

function addData(shift) {
now = [now.getFullYear(), now.getMonth() 1, now.getDate()].join('/');
date.push(now);
data.push((Math.random() - 0.4) * 10 data[data.length - 1]);

if (shift) {
date.shift();
data.shift();
}

now = new Date( new Date(now) oneDay);
}

for (var i = 1; i < 100; i ) {
addData();
}

option = {
xAxis: {
type: 'category',
boundaryGap: false,
data: date
},
yAxis: {
boundaryGap: [0, '50%'],
type: 'value'
},
dataZoom: [{
start: 70,
// zoomLock: true,
}],
series: [
{
name:'成交',
type:'line',
data: data
}
]
};

setInterval(function () {
for(var i=0;i<5;i ){
addData(true);
}
myChart.setOption({
xAxis: {
data: date
},
series: [{
name:'成交',
data: data
}]
});
}, 1000);

### What is expected?
正常渲染

### What is actually happening?
左侧出现两点连线不规则折断