title: ERROR [karma]: [TypeError: Cannot call method 'push' of undefined] when adding HTML output
body: <p>I'm using karma and jasmine for some unit testing.  I'd like an html output instead of checking the console / terminal and found this: <a href="https://www.npmjs.org/package/karma-htmlfile-reporter">https://www.npmjs.org/package/karma-htmlfile-reporter</a> which is perfect for my requirements.</p>
  
  <p>When I run it I get an error : </p>
  
  <pre><code>    `ERROR [karma]: [TypeError: Cannot call method 'push' of undefined]
      TypeError: Cannot call method 'push' of undefined
      at onBrowserStart (/usr/local/lib/node_modules/karma/lib/reporters/base.js:14:20)
      at null.&lt;anonymous&gt; (/usr/local/lib/node_modules/karma/lib/events.js:15:22)
      at EventEmitter.emit (events.js:117:20)
      at onStart (/usr/local/lib/node_modules/karma/lib/browser.js:128:13)
      at Socket.&lt;anonymous&gt; (/usr/local/lib/node_modules/karma/lib/events.js:15:22)
      at Socket.EventEmitter.emit [as $emit] (events.js:117:20)
      at SocketNamespace.handlePacket (/usr/local/lib/node_modules/karma/node_modules/socket.io/lib/namespace.js:335:22)
      at Manager.onClientMessage (/usr/local/lib/node_modules/karma/node_modules/socket.io/lib/manager.js:488:38)
      at WebSocket.Transport.onMessage (/usr/local/lib/node_modules/karma/node_modules/socket.io/lib/transport.js:387:20)
      at Parser.&lt;anonymous&gt; (/usr/local/lib/node_modules/karma/node_modules/socket.io/lib/transports/websocket/hybi-16.js:39:10)
  </code></pre>
  
  <p>I've hunted on google for an answer but yet to find one, if I remove the 'html' from the reports in the config it works fine.  I've not used jasmine / karma before so unsure where to look for help.</p>
  
  <p>The part of the config related to reports:     ` </p>
  
  <pre><code>   reporters: ['progress', 'html'],
  
    htmlReporter: {
        outputFile: 'tests/units.html'
    },``
  </code></pre>
  
  <p>Thanks for any assistance.</p>