Incorrect format string

[kmatzen]

https://github.com/seanbell/opensurfaces/blob/master/server/mturk/models.py#L237

base_url = 'http://' % settings.SERVER_IP

Missing the string placeholder. Change to either

base_url = 'http://%s' % settings.SERVER_IP

or

base_url = 'http://' + settings.SERVER_IP

Although, it doesn't really matter anymore since mturk outright rejects HITs that specify a URL with http://.