mail/spamassassin: Update to 3.4.2

Update mail/spamassassin to 3.4.2. This update includes security fixes.
For complete changelog and upgrade notes, see:
https://mail-archives.apache.org/mod_mbox/spamassassin-announce/201809.mbox/%3cc44ca0f1-cba9-b129-20b2-ba59816cfd13@apache.org%3e

Big thanks to Larry Rosenman (ler) for help with testing!

PR: 231412
Reported by: dewayne@heuristicsystems.com.au
Tested by: ler
MFH: 2018Q3
Security: 613193a0-c1b4-11e8-ae2d-54e1ad3d6335