解决办法

1. 命令行输入：npm run eject

2. 修改package.json文件中babel配置：
   "babel": {

      "presets": [
        "react-app"
      ],
      "plugins":[
        [
          "@babel/plugin-proposal-decorators",
          {
            "legacy":true
          }
        ],
        [
          "@babel/plugin-proposal-class-properties",
          {
            "loose":true
          }
        ]
      ]
   }