databases/mongodb36: update 3.6.17 -> 3.6.18

PR: 247394
Submitted by: Ronald Klop <ronald-lists@klop.ws>
Approved by: dev@dudu.ro (maintainer)
MFH: 2020Q2
Relnotes: https://docs.mongodb.com/manual/release-notes/3.6/#may-1-2020
Security: CVE-2020-7921