0. 使用的webpack环境
由于基于webpack4，因此这一步npm安装的包应为：
npm install --save-dev babel-loader@7 babel-core babel-plugin-transform-class-properties babel-plugin-transform-export-extensions babel-plugin-transform-object-rest-spread babel-preset-env babel-preset-react cross-env [email protected] html-webpack-plugin@4 netlify-cms react source-map-loader@1 style-loader@2 webpack@4 webpack-cli@4 webpack-serve