gcal-bot: Rename variable 'humbug'

It's weird to clobber the module, although it works.

(imported from commit 160d6e1c596ba6618c3da9c8cdc2f5cd3ca43dc6)

api/bots/gcal-bot

@@ -82,7 +82,7 @@ def get_calendar_url():
 
 calendar_url = get_calendar_url()
 
-humbug = humbug.Client(
+client = humbug.Client(
     email=options.user,
     api_key=options.api_key,
     site=options.site,
@@ -129,10 +129,10 @@ def send_reminders():
     else:
         message = 'Reminder:\n\n' + '\n'.join('* ' + m for m in messages)
 
-    humbug.send_message(dict(
-        type      = 'private',
-        to = options.user,
-        content   = message))
+    client.send_message(dict(
+        type    = 'private',
+        to      = options.user,
+        content = message))
 
     sent |= keys