do nightly build against stable Coq

.gitlab-ci.yml

@@ -37,15 +37,10 @@ build-coq.8.7.1:
     - build-time.txt
     - build-env.txt
 
-build-coq.8.6.1:
-  <<: *template
-  variables:
-    OPAM_PINS: "coq version 8.6.1   coq-mathcomp-ssreflect version 1.6.4"
-
 build-iris.dev:
   <<: *template
   variables:
-    OPAM_PINS: "coq version dev   coq-mathcomp-ssreflect version dev   coq-iris.dev git https://gitlab.mpi-sws.org/FP/iris-coq.git#$IRIS_REV"
+    OPAM_PINS: "coq version 8.7.1   coq-mathcomp-ssreflect version 1.6.4   coq-iris.dev git https://gitlab.mpi-sws.org/FP/iris-coq.git#$IRIS_REV"
   except:
   only:
   - triggers