Adds firefox driver in selenium-webdriver to allowed kwargs warning

This is fixed in 4.x branch. I've submitted a patch upstream to fix it
in 3.x which is what we are using here.

Upstream patch: https://github.com/SeleniumHQ/selenium/pull/9228

spec/deprecation_toolkit_env.rb

@@ -61,6 +61,7 @@ module DeprecationToolkitEnv
       batch-loader-1.4.0/lib/batch_loader/graphql.rb
       carrierwave-1.3.1/lib/carrierwave/sanitized_file.rb
       activerecord-6.0.3.4/lib/active_record/relation.rb
+      selenium-webdriver-3.142.7/lib/selenium/webdriver/firefox/driver.rb
     ]
   end