fix readme typo

Author: jochen-testingbot

README.md

@@ -133,7 +133,7 @@ Deletes/stops a specific tunnel for the current user
 
 
 ```python
-testingbotclient.tunnel.delete_tunnel(sessionId)
+testingbotclient.tunnel.delete_tunnel(tunnelId)
 ```
 
 ### uploadToStorage - Local File
@@ -198,4 +198,4 @@ python test_travis.py
 
 ## More documentation
 
-Check out the [TestingBot REST API](https://testingbot.com/support/api) for more information.
+Check out the [TestingBot REST API](https://testingbot.com/support/api) for more information.