title: Configuration.resolve has an unknown property 'root'
body: <p>I get the following error :</p>
  
  <blockquote>
    <p>Invalid configuration object. Webpack has been initialised using a
    configuration object that does not match the API schema.
     - configuration.resolve has an unknown property 'root'. These properties are valid:    object { alias?, aliasFields?,
    cachePredicate?, descriptionFiles?, enforceExtension?,
    enforceModuleExtension?, extensions?, fileSystem?, mainFields?,
    mainFiles?, moduleExtensions?, modules?, plugins?, resolver?,
    symlinks?, unsafeCache?, useSyncFileSystemCalls? }</p>
  </blockquote>
  
  <p>I use <a href="https://webpack.js.org/" rel="noreferrer">webpack 2.3.2</a>.</p>
  
  <hr>
  
  <p>My <strong>webpack.config.js</strong> looks like this :</p>
  
  <pre><code>module.exports= {
    entry:'./public/app.jsx',
    output: {
      path: __dirname,
      filename:'./public/bundle.js'
    },
    resolve: {
      root: __dirname,
      alias:{
        Mod1: 'public/components/mod1.jsx',
        Mod2:'public/components/mod2.jsx',
        Mod3: 'public/components/mod3.jsx'
      },
      extensions: ['*','.js','.jsx']
    },
    module :{
      loaders:[{
        loader :'babel-loader',
        query :{
          presets:['react','es2015','es2017']
        },
        test:/\.jsx?$/,
        exclude:/(node_modules|bower_components)/
      }]
    }
  };
  </code></pre>