[Appium]Get invisible elements

uiautomator2 start supporting findInvisibleElement.
https://github.com/appium/appium-uiautomator2-server/issues/61

After the following method, you can get invisible elements from uiautomator2.

update_settings allowInvisibleElements: true

https://github.com/appium/ruby_lib/blob/cc913edb4bc24c18a58c2c5490dfb7b5a705d303/lib/appium_lib/common/command.rb#L46