m4 dependency missing

 + Trying to install it in a job, generalise then if it works

.gitlab-ci.yml

@@ -6,6 +6,8 @@ stages:
 
 # OCaml version 4.02
 ocaml_402:
+  before_script: 
+    - sudo apk update && sudo apk add m4
   stage: test
   image: ocaml/opam:alpine_ocaml-4.02.3
   script: "./gitlab-ci.sh"