Update nginx docker container to use http2.

[smrubin]

Current nginx docker container is version 1.6.2 which does not support http2. We should update the nginx install for this image, or use another one with http2 enabled, and then add http2 back in to the nginx config file.

[smrubin]

Update: http2 configuration has been added with the recent upgrade of nginx version >= 1.9.5.

However, some modern browsers (namely Chrome) still won't serve over http2 due to the version of openssl being used and specifically that these browsers only support ALPN and have discontinued support for NPN. To support ALPN, we need at least openssl version 1.0.2, and Debian 8 (jessie) still uses 1.0.1k.

Until the docker version of Debian 8 (jessie) is updated, a new version of Debian is released, or the official nginx image is updated to use a newer version of openssl that supports ALPN, there is no easy fix to get http2 (currently a waiting game).

If we decide in the near future that serving http2 is a must, we can use jessie-backports inside the container. See the following links for resources:
https://ma.ttias.be/day-google-chrome-disables-http2-nearly-everyone-may-31st-2016/
nginxinc/docker-nginx#76
https://serverfault.com/questions/732474/nginx-configured-with-http2-doesnt-deliver-http-2
https://serverfault.com/questions/775298/debian-jessie-nginx-with-openssl-1-0-2-to-use-alpn-rather-than-npn
https://sergii.rocks/feed/post/nginx-http2-with-alpn-on-debian-8-jessie
https://michaelscott.uk/nginx-with-http2-and-alpn-debian