[rb] rename instance variable for clarity

Author: titusfortner

rb/lib/selenium/webdriver/common/driver.rb

@@ -69,7 +69,7 @@ def for(browser, opts = {})
       #
 
       def initialize(bridge: nil, listener: nil, **opts)
-        @service = nil
+        @service_manager = nil
         @devtools = nil
         bridge ||= create_bridge(**opts)
         add_extensions(bridge.browser)
@@ -172,7 +172,7 @@ def page_source
       def quit
         bridge.quit
       ensure
-        @service&.stop
+        @service_manager&.stop
         @devtools&.close
       end
 
@@ -330,8 +330,8 @@ def generate_capabilities(capabilities)
 
       def service_url(service)
         service ||= Service.send(browser)
-        @service = service.launch
-        @service.uri
+        @service_manager = service.launch
+        @service_manager.uri
       end
 
       def screenshot