title: Nightwatch.js: why do I get Unable to create new service: GeckoDriverService?
body: <p>I am trying to setup the latest nightwatch.js for the first time. This is my nightwatch.json:</p>
  
  <pre><code>{
    "src_folders" : ["tests"],
    "output_folder" : "reports",
    "custom_commands_path" : "",
    "custom_assertions_path" : "",
    "page_objects_path" : "",
    "globals_path" : "",
  
    "selenium" : {
      "start_process" : true,
      "server_path" : "selenium-server-standalone-3.8.1.jar",
      "log_path" : "",
      "port" : 4444,
      "cli_args" : {
        "webdriver.chrome.driver" : "",
        "webdriver.gecko.driver" : "",
        "webdriver.edge.driver" : ""
      }
    },
  
    "test_settings" : {
      "default" : {
        "launch_url" : "http://localhost",
        "selenium_port"  : 4444,
        "selenium_host"  : "localhost",
        "silent": true,
        "screenshots" : {
          "enabled" : false,
          "path" : ""
        },
        "desiredCapabilities": {
          "browserName": "firefox",
          "marionette": true
        }
      },
  
      "chrome" : {
        "desiredCapabilities": {
          "browserName": "chrome"
        }
      },
  
      "edge" : {
        "desiredCapabilities": {
          "browserName": "MicrosoftEdge"
        }
      }
    }
  }
  </code></pre>
  
  <p>When I run nightwatch I get this error:</p>
  
  <pre><code>Starting selenium server... started - PID:  3176
  
  [Go] Test Suite
  ===================
  
  Running:  Demo test
  
  Error retrieving a new session from the selenium server
  
  Connection refused! Is selenium server started?
  { value:
     { message: 'Unable to create new service: GeckoDriverService\nBuild info: ve
  sion: \'3.8.1\', revision: \'6e95a6684b\', time: \'2017-12-01T19:05:32.194Z\'\n
  ystem info: host: \'S0026COW1983\', ip: \'10.39.13.81\', os.name: \'Windows Ser
  er 2008 R2\', os.arch: \'x86\', os.version: \'6.1\', java.version: \'1.8.0_131\
  \nDriver info: driver.version: unknown',
       error: 'session not created' },
  </code></pre>
  
  <p>How can I resolve this?</p>