Update check to see if we are speaking to a W3C remote end point

specificationLevel is defined in http://w3c.github.io/webdriver/webdriver-spec.html#capabilities

Author: AutomatedTester

py/selenium/webdriver/remote/webdriver.py

@@ -139,7 +139,7 @@ def start_session(self, desired_capabilities, browser_profile=None):
         self.capabilities = response['value']
 
         # Quick check to see if we have a W3C Compliant browser
-        self.w3c = "takesElementScreenshot" in self.capabilities
+        self.w3c = "specificationLevel" in self.capabilities
 
     def _wrap_value(self, value):
         if isinstance(value, dict):