【报Bug】picker date模式，加了startdate和enddate后，选择有问题

[内容]
picker date模式，加了startdate和enddate，startdate为2019-01-27，enddate为2019-04-27，选择1月31号时，直接跳到4月27，选择不上1月31，选择2月1号时，有跳到了1月27，选择不上2月1日，用官方代码试验的。
重现步骤
[步骤]

<template>
<view>
<page-head :title="title"></page-head>
<view class="uni-title uni-common-pl">地区选择器</view>
<view class="uni-list">
<view class="uni-list-cell">
<view class="uni-list-cell-left">
当前选择
</view>
<view class="uni-list-cell-db">
<picker @change="bindPickerChange" :value="index" :range="array">
<view class="uni-input">{{array[index]}}</view>
</picker>
</view>
</view>
</view>

复制代码    <view class="uni-title uni-common-pl">时间选择器</view>  
    <view class="uni-list">  
        <view class="uni-list-cell">  
            <view class="uni-list-cell-left">  
                当前选择  
            </view>  
            <view class="uni-list-cell-db">  
                <picker mode="time" :value="time" start="09:01" end="21:01" @change="bindTimeChange">  
                    <view class="uni-input">{{time}}</view>  
                </picker>  
            </view>  
        </view>  
    </view>  

    <view class="uni-title uni-common-pl">日期选择器</view>  
    <view class="uni-list">  
        <view class="uni-list-cell">  
            <view class="uni-list-cell-left">  
                当前选择  
            </view>  
            <view class="uni-list-cell-db">  
                <picker mode="date" :value="date" :start="startDate" :end="endDate" @change="bindDateChange">  
                    <view class="uni-input">{{date}}</view>  
                </picker>  
            </view>  
        </view>  
    </view>  
</view>  

</template>
<script>
import {DateUtils} from './app.js'
export default {
data() {
const currentDate = this.getDate({
format: true
});
return {
title: 'picker',
array: ['中国', '美国', '巴西', '日本'],
index: 0,
date: currentDate,
time: '12:01'
}
},
computed: {
// startDate() {
// let a = DateUtils.toLong(DateUtils.addDays('2019-01-27', 1));
// console.log(a);
// return a;
// },
// endDate() {
// let b = DateUtils.toLong(DateUtils.addDays('2019-01-27',7));
// console.log(b);
// return b;
// }
startDate() {
// let a = DateUtils.toLong(DateUtils.addDays('2019-01-27', 1));
// console.log(a);
let a = this.getDate('start');
console.log(a);
return a;
},
endDate() {
// let b = DateUtils.toLong(DateUtils.addDays('2019-01-27',90));
let b = this.getDate('end');
console.log(b);
return b;
}
},
methods: {
bindPickerChange: function(e) {
console.log('picker发送选择改变，携带值为', e.target.value)
this.index = e.target.value
},
bindDateChange: function(e) {
this.date = e.target.value
},
bindTimeChange: function(e) {
this.time = e.target.value
},
getDate(type) {
const date = new Date();

复制代码            let year = date.getFullYear();  
            let month = date.getMonth() + 1;  
            let day = date.getDate();  

            if (type === 'start') {  
                // year = year - 60;  
                day = day;  
            } else if (type === 'end') {  
                // year = year + 2;  
                month = month + 3;  
            }  
            month = month > 9 ? month : '0' + month;;  
            day = day > 9 ? day : '0' + day;  

            return `${year}-${month}-${day}`;  
        }  
    }  
}  

</script>

<style>

</style>
[结果]
[期望]
[如果语言难以表述清晰，可以拍一个视频或截图，有图有真相]

IDE运行环境说明
HBuilderX]
[IDE版本号]
HBuilderX 1.3.2 20181214
[windows版本号]
window 7
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