www/node6: Update 6.11.4 -> 6.11.5

Update to the latest upstream v6.x release to address a remote DoS
vulnerability.

https://nodejs.org/en/blog/vulnerability/oct-2017-dos/
https://nodejs.org/en/blog/release/v6.11.5/

Approved by: robak (mentor)
MFH: 2017Q4
Security: CVE-2017-14919
Differential Revision: https://reviews.freebsd.org/D12784