I have this code in my Cucumber Hooks file to run the ghost driver it was working until yesterday I start seeing the error message:
Before do
Selenium::Web
For those who encounter this error, you can work around it by locking your selenium-webdriver version in your Gemfile like so:
gem 'selenium-webdriver', '~> 3.6.0'
and then bundle update to downgrade.
(You may not even have selenium-webdriver specified in your Gemfile currently if it's just being loaded as a dependency of watir or some other library.)
The long term fix, of course, is to move off of PhantomJS to Chrome or Firefox headless.