mendeley has hard version requirements across the board (== instead of >=), many/all of which are now grossly out of date (requests being the most notable example). With the new pip dependency manager, we can no longer effectively replace these requirements: https://mail.python.org/archives/list/pypi-announce@python.org/thread/DIWIYIMGAOHDWQXXUZW44YRSW7UYQ4CA/
As a result, our build is now broken, and I'm assuming we're not alone.
Please update your dependencies ASAP.