I am new to Nightwatch and I am trying to run this command 

> 
> $ nightwatch --env gecko /tests/test1/sample1.js
> 
> 
> 

I am trying to figure out how to select a browser from the nightwatch.json file via command line. 

Here's my conf file. I was reading the tutorial on Nightwatch.js and I can't seem to find this set up.

```
{
"src_folders": [
    "tests"
],
"selenium": {
    "start_process": false,
    "server_path": "bin/selenium-server-standalone-2.53.1.jar",
    "log_path": "",
    "host": "127.0.0.1",
    "port": 4444,
    "cli_args": {
        "webdriver.chrome.driver": "bin/chromedriver",
        "webdriver.gecko.driver" : "bin/geckodriver"
    }
},
"test_settings": {
    "default": {
        "launch_url": "http://127.0.0.1/",
        "selenium_port": 4444,
        "selenium_host": "localhost",
        "silent": true,
        "screenshots": {
            "enabled": false,
            "path": ""
        },
        "desiredCapabilities": {
            "browserName": "chrome",
            "javascriptEnabled": true,
            "acceptSslCerts": true
        }
    }
    "gecko": {
    "launch_url": "http://127.0.0.1/",
    "selenium_port": 4444,
    "selenium_host": "localhost",
    "silent": true,
    "screenshots": {
        "enabled": false,
        "path": ""
    },
    "desiredCapabilities": {
        "browserName": "gecko",
        "javascriptEnabled": true,
        "acceptSslCerts": true
        }
    }
}
}

```

The error message I get is 

```
Error: No testing environment specified.
    at CliRunner.parseTestSettings (/usr/local/lib/node_modules/nightwatch/lib/runner/cli/clirunner.js:515:13)
    at CliRunner.setup (/usr/local/lib/node_modules/nightwatch/lib/runner/cli/clirunner.js:49:8)
    at Object.exports.runner (/usr/local/lib/node_modules/nightwatch/lib/index.js:551:17)
    at /usr/local/lib/node_modules/nightwatch/bin/runner.js:10:16
    at Object.exports.cli (/usr/local/lib/node_modules/nightwatch/lib/index.js:545:5)
    at Object.<anonymous> (/usr/local/lib/node_modules/nightwatch/bin/runner.js:8:14)
    at Module._compile (module.js:571:32)
    at Object.Module._extensions..js (module.js:580:10)
    at Module.load (module.js:488:32)
    at tryModuleLoad (module.js:447:12)

```