nightwatch stuck on starting selenium server

I'm using nightwatch.js to test website.
2 days ago, It worked, but since tomorrow It didn't work.
When I'm trying to test with $ nightwatch <test_file> (because I installed nightwatch globally. and It worked for a month.), It shows Starting selenium server... and don't anything.
using --verbose doesn't show anything else. It also just shows Starting selenium server... I updated chromedriver, nightwatch and npm, but same.

I'm using Ubuntu 16.04.1 LTS, amd64
chromedriver_linux64.zip
nightwatch 0.9.14
selenium-server-standalone-3.3.1


this is my nightwatch.json

{
  "src_folders" : ["tests/e2e"],
  "output_folder" : "tests/reports",
  "custom_commands_path" : "tests/custom",
  "custom_assertions_path" : "",
  "page_objects_path" : "",
  "globals_path" : "",
  "selenium" : {
    "start_process" : true,
    "server_path" : "./bin/selenium-server-standalone-3.3.1.jar",
    "log_path" : "tests/logs",
    "host" : "127.0.0.1",
    "port" : 4444,
    "cli_args" : {
      "webdriver.chrome.driver" : "./chromedriver",
      "webdriver.ie.driver" : ""
    }
  },
  "test_settings" : {
    "default" : {
      "launch_url" : "http://localhost",
      "selenium_port"  : 4444,
      "selenium_host"  : "localhost",
      "silent": true,
      "screenshots": {
        "enabled" : true,
        "on_failure" : true,
        "on_error" : false,
        "path" : "tests/screenshots"
      },
      "desiredCapabilities": {
        "browserName": "chrome",
        "javascriptEnabled": true,
        "acceptSslCerts": true
      }
    }
  }
}

via errorMessage