Clean up README

Author: gcatanese

README.md

@@ -91,11 +91,6 @@ response = adyen.checkout.payments_api.payments({
 })
 ~~~~
 
-- Change API Version
-~~~~ruby
-adyen.checkout.version = 69
-~~~~
-
 ### Example integration
 
 For a closer look at how our Ruby library works, clone our [example integration](https://github.com/adyen-examples/adyen-rails-online-payments). This includes commented code, highlighting key features and concepts, and examples of API calls that can be made using the library.