Fix get_issuer/subject docstrings for X509 too.
Fix get_issuer/subject docstrings for X509 too.

reaperhulk/pyopenssl,mitghi/pyopenssl,hynek/pyopenssl,pyca/pyopenssl,mitghi/pyopenssl,mhils/pyopenssl,hynek/pyopenssl,mhils/pyopenssl,reaperhulk/pyopenssl