title: Setup external libraries with laravel mix
body: <p>I need to use an external library on web pack with laravel-mix. On web pack I should do something like this <em>as described in the <a href="https://webpack.github.io/docs/library-and-externals.html" rel="noreferrer">webpack docs</a></em>  </p>
  
  <pre><code>{
      output: {
          // export itself to a global var
          libraryTarget: "var",
          // name of the global var: "Foo"
          library: "Foo"
      },
      externals: {
          // require("jquery") is external and available
          //  on the global var jQuery
          "jquery": "jQuery"
      }
  }
  </code></pre>
  
  <p>But I can do this with laravel mix?</p>