Webpack: Unknown argument: mode / configuration has an unknown property 'mode' : <p>getting crazy with this, really missing something....</p>

<p>I have webpack 4.6.0, webpack-cli ^2.1.2, so the latest. </p>

<p>Following the docs (<a href="https://webpack.js.org/concepts/mode/" rel="noreferrer">https://webpack.js.org/concepts/mode/</a>), want to use the mode to have to configs, one for production and one for development, but I get:</p>

<p>configuration[0] has an unknown property 'mode'. These properties are valid:
   object { amd?, bail?, cache?, context?, dependencies?, devServer?, devtool?, entry, externals?, loader?, module?, name?, node?, output?, parallelism?, performance?, plugins?, profile?, recordsInputPath?, recordsOutputPath?, recordsPath?, resolve?, resolveLoader?, stats?, target?, watch?, watchOptions? }</p>

<p>What am I missing :O????? </p>

<pre><code>module.exports = [
  merge(base, {
    mode: 'development',
    output: {
      path: path.resolve(__dirname, './public/assets/development'),
    },
  }),
  merge(base, {
    mode: 'production',
    output: {
      path: path.resolve(__dirname, './public/assets/production'),
      filename: '[name].bundle.js',
    },
  }),
]
</code></pre>
