Replace comment references to trac.humbughq.com with trac.zulip.net

(imported from commit 231d0884345be525d58ce51f48a76bba6960f09d)

tools/run-dev.py

@@ -10,7 +10,7 @@ from twisted.internet import reactor
 from twisted.web      import proxy, server, resource
 
 # Monkey-patch twisted.web.http to avoid request.finish exceptions
-# https://trac.humbughq.com/ticket/1728
+# https://trac.zulip.net/ticket/1728
 from twisted.web.http import Request
 orig_finish = Request.finish
 def patched_finish(self):

zerver/lib/bugdown/__init__.py

@@ -743,7 +743,7 @@ def do_convert(md, realm_domain=None, message=None):
     try:
         # Spend at most 5 seconds rendering.
         # Sometimes Python-Markdown is really slow; see
-        # https://trac.humbughq.com/ticket/345
+        # https://trac.zulip.net/ticket/345
         return timeout(5, _md_engine.convert, md)
     except:
         from zerver.lib.actions import internal_send_message