Launch safari using appium

launch_safari.rb

require 'selenium-webdriver'

capabilities = {
  'browserName' => 'iOS',
  'platform' => 'Mac',
  'version' => '6.1',
  'app' => 'Safari'
}

# Started Appium using appium app.
# server  = 127.0.0.1
# port = 4723
# UDID = valid UDID

server_url = "http://127.0.0.1:4723/wd/hub"
@driver = Selenium::WebDriver.for(:remote, :desired_capabilities => capabilities, :url => server_url)
sleep 5
@driver.get "http://www.google.com"

# Output
# /Users/demo/.rvm/gems/ruby-1.9.3-p429/gems/selenium-webdriver-2.35.1/lib/selenium/webdriver/remote/response.rb:51:in `assert_ok': A session is either terminated or not started (Selenium::WebDriver::Error::NoSuchDriverError)