Update gitlab-ci.sh

Tress are not displayed with ci (maybe tree is not installed).

gitlab-ci.sh

@@ -14,10 +14,10 @@ eval `opam config env`
 
 # Versions and files
 echo "Trees"
-echo "."
-tree .
+echo "$PWD"
+ls .
 echo "~"
-tree ~
+ls ~
 echo "= Versions ="
 echo "opam --version"
 opam --version