iOS10

iOS10打包后页面报错，白屏
SyntaxError: Cannot declare a let variable twice

Swiper插件中用到了ES6的语法a = b ** c，a是b的c次方，而iOS 10的Safari里不认识这样的语法

https://www.jianshu.com/p/ec7b582ec77c

https://segmentfault.com/a/1190000013075464

https://github.com/nolimits4web/swiper/issues/2263