www/node6: Update 6.15.1_1 -> 6.16.0

The 6.15.0 security release introduced some unexpected breakages on the
6.x release line. This is a special release to fix a regression in the
HTTP binary upgrade response body and add a missing CLI flag to adjust
the max header size of the http parser.

https://nodejs.org/en/blog/release/v6.16.0/

Sponsored by: Miles AS