wiki does not support ucuserprefix for API:Usercontribs which is strange because it was introduced in mw 1.13+ and wikia has Version 1.19.24
```
>>> import pwb, pywikibot as py
>>> s = py.Site()
>>> s
APISite("wikia", "wikia")
>>> s.mw_version
MediaWikiVersion ('1.19.24')
>>> gen = s.usercontribs(userprefix='John', total=1)
>>> x = next(iter(gen))
WARNING: API error ucnouser: The user parameter must be set
Traceback (most recent call last):
File "<pyshell#6>", line 1, in <module>
x = next(iter(gen))
File "pywikibot\data\api.py", line 2968, in __iter__
self.data = self.request.submit()
File "pywikibot\data\api.py", line 2269, in submit
raise APIError(**result['error'])
APIError: ucnouser: The user parameter must be set
```
See also https://api.travis-ci.org/v3/job/481858524/log.txt
The following tests are failing due to this issue:
- tests.site_tests.TestUserContribsWithoutUser testMethod=test_user_prefix
- tests.site_tests.TestUserContribsWithoutUser testMethod=test_user_prefix_range
- tests.site_tests.TestUserContribsWithoutUser testMethod=test_user_prefix_reverse