use a more precise version of docker image, to lock ocaml version used and avoid installation problem for ocsigenserver.2.9
use a more precise version of docker image, to lock ocaml version used and avoid installation problem for ocsigenserver.2.9

glondu/belenios,glondu/belenios,glondu/belenios,glondu/belenios,glondu/belenios