title: Unexpected token: operator (>) from UglifyJs
body: <p>I have 2 Vue-Cli webpack projects (ClientApp and Lib).
  Lib is my components library (shared with other projects)</p>
  
  <h3>Problem</h3>
  
  <p>When I build my project ClientApp <code>npm run build</code>, I have the following error:</p>
  
  <pre><code>ERROR in static/js/app.d08a24ce0e8d0438ce68.js from UglifyJs
  Unexpected token: operator (&gt;) [C:/.../Lib/src/tools/escape-key.js:3,0][static/js/app.d08a24ce0e8d0438ce68.js:17468,38]
  </code></pre>
  
  <h3>Questions</h3>
  
  <p>It seems like the error comes from an arrow function in the file <code>escape-key.js</code>.
  This is ES6 syntax and UglifyJS can't parse this.
  Shouldn't Babel go first, before Uglify?
  Note that is works well with <code>*.vue</code> files.</p>
  
  <h3>Project structure</h3>
  
  <pre><code>ClientApp
     | - build
     | - config
     | - src
         | - App.Vue // import EscapeKey from '~lib/tools/escape-key';
  
  
  
  Lib
    | -src
       | - tools
           | - escape-key.js
  </code></pre>
  
  <h3>ClientApp's webpack.base.conf.js file</h3>
  
  <p>Note there is an alias to Lib.</p>
  
  <pre><code>resolve: {
      extensions: ['.js', '.vue', '.json'],
      alias: {
        '@': resolve('src'),
        '~lib': path.join(__dirname, '../../lib/src'),
      }
    },
  </code></pre>
  
  <p>Please feel free to ask for more details if required.</p>