There is an conflict with textproc/py-commonmark and textproc/cmark. Looks like bin/cmark was added by the last py-commonmark update.
Collision in cmark-0.29.0: the following files already exist /usr/local/bin/cmark (py3-commonmark-0.9.1 and cmark-0.29.0) Couldn't install cmark-0.29.0