Support HTTP2

[rasodu]

https://assets.wp.nginx.com/wp-content/uploads/2015/09/NGINX_HTTP2_White_Paper_v4.pdf

• Requires that site use SSL. (Not requirement of HTTP2 but most most web browser will only use HTTP2 for SSL website)
• Use nginx 1.9.5 or greater
• OpenSSL 1.0.2 or later
• Add 'http2' to nginx config

[rasodu]

Steps to complete this

• Upgrade NGINX image used in dockerfile
• Add 'http2' in nginx config
• Add unittest if possible

[rasodu]

Everything is done except for unittest. Tag will be changed to bug because of the lake of unittest.