Nginx configured with http2 doesn’t deliver HTTP/2

I have a problem with my Nginx configuration. I upgraded to nginx 1.9.6 to test http/2 but it does not work on my server.

I used ubuntu 14.04.2 LTS

This is the nginx -V output :

nginx version: nginx/1.9.6
built with OpenSSL 1.0.2d 9 Jul 2015
TLS SNI support enabled
configure arguments: --prefix=/etc/nginx --conf-path=/etc/nginx/nginx.conf --error-log-path=/var/log/nginx/error.log --http-client-body-temp-path=/var/lib/nginx/body --http-fastcgi-temp-path=/var/lib/nginx/fastcgi --http-log-path=/var/log/nginx/access.log --http-proxy-temp-path=/var/lib/nginx/proxy --http-scgi-temp-path=/var/lib/nginx/scgi --http-uwsgi-temp-path=/var/lib/nginx/uwsgi --lock-path=/var/lock/nginx.lock --pid-path=/var/run/nginx.pid --with-pcre-jit --with-debug --with-http_addition_module --with-http_auth_request_module --with-http_dav_module --with-http_geoip_module --with-http_gzip_static_module --with-http_image_filter_module --with-http_realip_module --with-http_stub_status_module --with-http_ssl_module --with-http_sub_module --with-http_xslt_module --with-http_v2_module --with-stream --with-ipv6 --with-mail --with-mail_ssl_module --with-openssl=/build/nginx-GFP362/nginx-1.9.6/debian/openssl-1.0.2d --add-module=/build/nginx-GFP362/nginx-1.9.6/debian/modules/nginx-auth-pam --add-module=/build/nginx-GFP362/nginx-1.9.6/debian/modules/nginx-echo --add-module=/build/nginx-GFP362/nginx-1.9.6/debian/modules/nginx-upstream-fair --add-module=/build/nginx-GFP362/nginx-1.9.6/debian/modules/nginx-dav-ext-module --add-module=/build/nginx-GFP362/nginx-1.9.6/debian/modules/nginx-cache-purge

And this is my vhost config :

server {
    listen         80;
    server_name    localhost;
    return         301 https://$server_name$request_uri;
}

server {
    listen 443 ssl http2; ## listen for ipv4; this line is default and implied

    root /var/www/rendez-vous;
    index index.phtml index.html index.htm;

    # Make site accessible from http://localhost/
    server_name localhost;
    ssl_certificate /etc/nginx/certificates/myeventsportal/server.crt;
    ssl_certificate_key /etc/nginx/certificates/myeventsportal/server.key;

/...

If I navigate to my site with the latest version of chrome, it is only served over http/1.1.