title: Why doesn't nightwatch pickup my browser configuration
body: <p>I am using nightwatch for testing a web site. Below is my configuration file. I want to use phantomjs as the browser so it can be run without open a browser. But when I run the tests with <code>nightwatch -c integration-tests/nightwatch.json</code> command, it always open my chrome browser. And I tried to modify the value for <code>browserName</code> and found out that whatever I put in doesn't have any effect. Is there anything wrong with my configuration?</p>
  
  <pre><code>{
    "src_folders": [
      "./integration-tests/tests"
    ],
    "output_folder": "./integration-tests/reports",
    "custom_commands_path": "",
    "custom_assertions_path": "",
    "page_objects_path": "",
    "globals_path": "",
    "selenium": {
      "start_process": false
    },
    "test_settings": {
      "default": {
        "launch_url": "http://localhost:9091",
        "selenium_port": 9515,
        "selenium_host": "localhost",
        "default_path_prefix": "",
        "silent": true,
        "screenshots": {
          "enabled": false,
          "path": ""
        },
        "desiredCapabilities": {
          "browserName": "phantomjs",
          "javascriptEnabled" : true,
          "phantomjs.binary.path" :"node_modules/phantomjs",
          "phantomjs.cli.args" : []
        }
      }
    }
  }
  </code></pre>