轮播图无法填充满宽度


```js
render() {
return (


{
this.state.imgUrls.map((item, idx) => (



))
}


)
}
```

index.scss
```
@import "~taro-ui/dist/style/components/flex.scss";
```

**期望行为**
图片能自适应填满宽度

**系统信息**
```
👽 Taro v3.2.8

Taro CLI 3.2.8 environment info:
System:
OS: macOS 11.3.1
Shell: 5.8 - /bin/zsh
Binaries:
Node: 15.14.0 - ~/.nvm/versions/node/v15.14.0/bin/node
Yarn: 1.22.10 - /opt/homebrew/bin/yarn
npm: 7.13.0 - ~/.nvm/versions/node/v15.14.0/bin/npm
npmPackages:
@tarojs/cli: 3.2.8 => 3.2.8
@tarojs/components: 3.2.8 => 3.2.8
@tarojs/mini-runner: 3.2.8 => 3.2.8
@tarojs/react: 3.2.8 => 3.2.8
@tarojs/runtime: 3.2.8 => 3.2.8
@tarojs/taro: 3.2.8 => 3.2.8
@tarojs/webpack-runner: 3.2.8 => 3.2.8
babel-preset-taro: 3.2.8 => 3.2.8
eslint-config-taro: 3.2.8 => 3.2.8
react: ^17.0.0 => 17.0.2
taro-ui: ^3.0.0-alpha.3 => 3.0.0-alpha.10
```