2018-12-26, Version 8.15.0 'Carbon' (LTS)

The 8.14.0 security release introduced some unexpected breakages on
the 8.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.

Notable changes:

* cli:
  - add --max-http-header-size flag (cjihrig)
    https://github.com/nodejs/node/pull/24811
* http:
  - add maxHeaderSize property (cjihrig)
    https://github.com/nodejs/node/pull/24860

PR-URL: https://github.com/nodejs/node/pull/25177