fixed invalid python

you can't use a positional argument after a keyword argument

Author: cronoik

articles/cognitive-services/Bing-Web-Search/includes/quickstarts/web-search-client-library-python.md

@@ -90,7 +90,7 @@ If the response contains web pages, images, news, or videos, the first result fo
     subscription_key = "YOUR_SUBSCRIPTION_KEY"
 
     # Instantiate the client and replace with your endpoint.
-    client = WebSearchClient(endpoint="YOUR_ENDPOINT", CognitiveServicesCredentials(subscription_key))
+    client = WebSearchClient(endpoint="YOUR_ENDPOINT", credentials=CognitiveServicesCredentials(subscription_key))
 
     # Make a request. Replace Yosemite if you'd like.
     web_data = client.web.search(query="Yosemite")