mail/phpmailer: Update to 5.2.18

• Update to 5.2.18
• Adjust pkg-plist for new release
• Remove LICENSE install from DOCS option
• Fix Remote Code Execution vulnerability

PR: 215576
Approved by: ports-secteam (amdmi3)
MFH: 2016Q4
Security: CVE-2016-10033
Security: c7656d4c-cb60-11e6-a9a5-b499baebfeaf