Add HSTS header regardless of status code
Add HSTS header regardless of status code

See nginx [doc](http://nginx.org/en/docs/http/ngx_http_headers_module.html#add_header) and [blog](https://www.nginx.com/blog/http-strict-transport-security-hsts-and-nginx/).
jwilder/nginx-proxy,kamermans/nginx-proxy,jwilder/nginx-proxy,kamermans/nginx-proxy,itsafire/nginx-proxy,itsafire/nginx-proxy