As of finishing DM-14828 we are now using pybind11 2.2.x instead of 2.1.x. This is a significant upgrade: the old macro PYBIND11_PLUGIN is replaced by the simpler PYBIND11_MODULE and code that makes explicit wrappers for __init__ and __getstate__/__setstate__ should be rewritten for safety and to avoid compiler warnings. All this and more is explained in the pybind11 upgrade guide. The LSST DM code has all been updated and there is a ticket branch for qserv which will require some work to make Travis happy. I have not touched sims code.