fix Coq version number

.gitlab-ci.yml

@@ -57,10 +57,10 @@ build-coq.8.7.dev:
   except:
   - triggers
 
-build-coq.8.7:
+build-coq.8.7.0:
   <<: *template
   variables:
-    OPAM_PINS: "coq version 8.7   coq-mathcomp-ssreflect version 1.6.2"
+    OPAM_PINS: "coq version 8.7.0   coq-mathcomp-ssreflect version 1.6.2"
   except:
   - triggers