Fix serialization of general comments for webhooks.
Review Request #8180 — Created May 23, 2016 and submitted
The code that serialized reviews for notifications was using a resource name
for general comments that didn't exist. This change fixes that.
Ran into errors when building the docs. After this change, no more errors.
Tool: PEP8 Style Checker Processed Files: reviewboard/notifications/webhooks.py Tool: Pyflakes Processed Files: reviewboard/notifications/webhooks.py