title: map is not a function in IE11
body: <p>I think a sneaky bug in IE11 is creeping in and breaking Dropzone. Line 1653:</p>
  
  <pre><code>key: "handleFiles",
      value: function handleFiles(files) {
      var _this5 = this;
  
      return files.map(function (file) {
          return _this5.addFile(file);
      });
  }
  </code></pre>
  
  <p>In IE11, if you call <code>typeof(files)</code>, you'll just get object - not array. It does have a length property, but, little else. No map function. <code>files.map(...</code> throws an exception.</p>