[opam] update dev-repo URL to Gitlab daily mirror

opam/opam

@@ -48,7 +48,7 @@ authors: [
 ]
 homepage: "http://frama-c.com/"
 license: "GNU Lesser General Public License version 2.1"
-dev-repo: "git+https://github.com/Frama-C/Frama-C-snapshot.git#latest"
+dev-repo: "git+https://git.frama-c.com/pub/frama-c.git"
 doc: "http://frama-c.com/download/user-manual-20.0-Calcium.pdf"
 bug-reports: "https://bts.frama-c.com/"
 tags: [