frontmatter-webpack-config.js

{ 
  build: {
    /*
    ** You can extend webpack config here
    */
    extend(config, ctx) {
      config.module.rules.push({
        test: /\.md$/,
        include: [path.resolve(__dirname, 'posts'), path.resolve(__dirname, 'blog')],
        loader: 'frontmatter-markdown-loader'
      })
    }
  }