According to GitHub - titusfortner/webdrivers: Keep your Selenium WebDrivers updated automatically, it will install an appropriate driver when you instantiate a corresponding Selenium WebDriver instance if you require 'webdrivers' first. But AFAICS, you never do that.
Moreover, some of your gemspecs require chromedriver-helper which has been discontinued in favor of webdrivers. So I guess it worked when that old gem was still working.