lang/python37: Fix security issues

The patches for CVE-2019-18348 and CVE-2020-8492 are in the 3.7 branch
and will be present on the next release.

Patch for applying CVE-2020-8492 fix here in the ports tree was reported
and submitted by Dani <i.dani@outlook.com>.

PR: 246808
MFH: 2020Q2
X-MFH-with: 536770, 536776
Security: ca595a25-91d8-11ea-b470-080027846a02 (CVE-2019-18348)
Security: a27b0bb6-84fc-11ea-b5b4-641c67a117d8 (CVE-2020-8492)