Log Message:
py-pyrsistent: update to 0.16.0.

0.16.0, 2020-03-24
 * No major updates but Python 2 support no longer guaranteed.
 * Fix #192, 'ignore_extra' for 'pvector_field'. Thanks @ss18 for this!
 * Fix #191, include LICENCE in distribution. Thanks @johnthagen for this!
 * Fix #190, minor MyPy errors. Thanks @Qhesz for this!