CI: rename jobs for consistency

.gitlab-ci.yml

@@ -23,14 +23,14 @@ variables:
   - master
   - /^ci/
 
-build-coq8.7:
+build-coq.8.7:
   <<: *template
   variables:
     OPAM_PINS: "coq version 8.7.dev   coq-mathcomp-ssreflect version dev"
   except:
   - triggers
 
-build-coq8.6.1:
+build-coq.8.6.1:
   <<: *template
   variables:
     OPAM_PINS: "coq version 8.6.1   coq-mathcomp-ssreflect version 1.6.1"