picker只能点击，不能滑动

[944zhang]

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Describe the bug
vue-template-compiler和vue都已经升级到2.6.10。
打开vant官方demo，基础组件->popup弹出层->底部弹出，picker只能点击，不能滑动。

Screenshots
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Environment

• Device: ios 10.3.3
• Browser: 微信
• Vant Version: 1.6.5

Reproduce
Provide the steps to reproduce and if possible a minimal demo of the problem via jsfiddle.
https://jsfiddle.net/dfarLdko/522/

[leemoncn]

你需要从后台杀死微信程序（或者safari），然后再打开，就好了。

[944zhang]

你需要从后台杀死微信程序（或者safari），然后再打开，就好了。

不行

[chenjiahan]

重复 issue：#3015