taro框架中使用时，图形画出来尺寸不对，设置pixelRatio也无效

• I have searched the issues of this repository and believe that this is not a duplicate.

Reproduction link

https://github.com/kevin82008/tas-taro-f2

Steps to reproduce

1. 执行yarn安装依赖

yarn add @tarojs/cli global
yarn

1. 执行 npm run dev 编译

npm run dev

1. 在微信小程序里查看效果