title: grunt uglify does not accept lambda or arrow functions
body: <p>I am running grunt-contrib-uglify v 2.15.1. It fails when I use a lambda or arrow function with:</p>
  
  <pre><code>Running "uglify:admin" (uglify) task
  { message: 'SyntaxError: Unexpected token: operator (&gt;)',
    filename: 'admin-app-ng.js',
    line: 4927,
    col: 50,
    pos: 216049,
    stack: 'Error\n    at new JS_Parse_Error (eval at &lt;anonymous&gt;
  </code></pre>
  
  <p>If I remove the lambda then the uglify functions.
  Is there a way to use uglify when using lambdas/arrow functions?</p>
  
  <p>This is the arrow function:</p>
  
  <pre><code>myService.getActions($scope.myVar, (type) =&gt; (type === 'myType')?true:false);
  </code></pre>