Update Dockerfile to use Flocq 3.1, disable Coq 8.7

Dockerfile

@@ -18,15 +18,16 @@ RUN cd /home/opam/opam-repository && git pull && cd
 RUN opam repo add coq-released https://coq.inria.fr/opam/released --set-default && \
     opam update
 
-#Install coq 8.7.2 in a switch
-RUN opam switch create coq8.7.2 ocaml-base-compiler.4.05.0 && \
-    eval `opam config env`
+### Currently disabled because some lemmas are missing in 8.7.2
+##Install coq 8.7.2 in a switch
+#RUN opam switch create coq8.7.2 ocaml-base-compiler.4.05.0 && \
+#    eval `opam config env`
 
-RUN opam install coq.8.7.2 coq-flocq.2.6.1
+#RUN opam install coq.8.7.2 coq-flocq.2.6.1
 
 #Install coq 8.8 in a switch
 RUN opam switch create coq8.8 ocaml-base-compiler.4.05.0
-RUN opam install coq.8.8.2 coq-flocq.2.6.1
+RUN opam install coq.8.8.2 coq-flocq.3.1.0
 
 # Install polyml from git
 RUN git clone https://github.com/polyml/polyml.git polyml && \