app.yaml s/python/nodejs in comment (#562)

Minor nit surfaced in bug

Author: llatif

appengine/hello-world/app.yaml

@@ -18,7 +18,7 @@ env: flex
 # This sample incurs costs to run on the App Engine flexible environment. 
 # The settings below are to reduce costs during testing and are not appropriate
 # for production use. For more information, see:
-# https://cloud.google.com/appengine/docs/flexible/python/configuring-your-app-with-app-yaml
+# https://cloud.google.com/appengine/docs/flexible/nodejs/configuring-your-app-with-app-yaml
 manual_scaling:
   instances: 1
 resources: