I don't see anything in this port which binds it to python2. I've just built successfully against python3.6. I notice that upstream just did the work to even support python 3.7.
A commit references this bug: Author: swills Date: Mon Jul 2 12:55:24 UTC 2018 New revision: 473730 URL: https://svnweb.freebsd.org/changeset/ports/473730 Log: devel/py-jira: allow build/usage with python 3 PR: 229462 Changes: head/devel/py-jira/Makefile
Committed, thanks!