title: Webpack-merge not accessing common configuration variables
body: <p>As I understand, webpack-merge helps us break down our webpack.config file into more manageable chunks, adding configuration relevant to the environment.</p>
  
  <blockquote>
    <p>While we will separate the production and development specific bits
    out, note that we'll still maintain a "common" configuration to keep
    things DRY. In order to merge these configurations together, we'll use
    a utility called webpack-merge. With the "common" configuration in
    place, we won't have to duplicate code within the environment-specific
    configurations. <br>
    - <em>Webpack - production</em></p>
  </blockquote>
  
  <p>My code in my <code>webpack.prod.js</code> is like so:</p>
  
  <pre><code>const merge = require('webpack-merge');
  const common = require('./webpack.common.js');
  
  module.exports = merge(common, {
    mode: 'production',
    devtool: 'source-map',
    module: {
      rules: [
        {
          test: /\.(png|svg|jpg|gif)$/,
          use: [
              'file-loader'
          ],
          exclude: [
            path.resolve(__dirname, "node_modules") //NEED TO ACCCESS PATH VARIABLE HERE
          ]
        }
    ]
  }
  </code></pre>
  
  <p>In my <code>webpack.common.js</code> is the variable <code>path</code> in which I thought <code>webpack.prod.js</code> has access to. I'm assuming it doesn't as I am presented with an error: </p>
  
  <pre><code>ReferenceError: path is not defined
  </code></pre>
  
  <p><strong><em>Question</em></strong></p>
  
  <p>How do I access the common configuration? Have I misunderstood the concept of <code>webpack-merge</code>?</p>