Update window switching key if it hits a spec compliant browser

Author: AutomatedTester

py/selenium/webdriver/remote/switch_to.py

@@ -87,6 +87,6 @@ def window(self, window_name):
             driver.switch_to.window('main')
         """
         data = {'name': window_name}
-        if self._driver.capabilities['marionette'] == True:
+        if self._driver.capabilities['w3c'] == True:
             data = {'handle': window_name}
         self._driver.execute(Command.SWITCH_TO_WINDOW, data)