There appears to be a server side problem with the memento webcite timegate
https://github.com/mementoweb/py-memento-client/issues/5
Causing problems with our tests - they skip rather than fail, but it means the tests are not operating.
https://travis-ci.org/wikimedia/pywikibot-core/jobs/113989338#L3329
https://ci.appveyor.com/project/wikimedia/pywikibot-core/build/1.0.823/job/yoy536ofag8fw46u#L4301