[opam] Correct dev-repos URL so it works with dune-release

Author: ejgallego

ppx_import.opam

@@ -8,7 +8,7 @@ homepage: "https://github.com/ocaml-ppx/ppx_import"
 doc: "https://ocaml-ppx.github.io/ppx_import/"
 license: "MIT"
 bug-reports: "https://github.com/ocaml-ppx/ppx_import/issues"
-dev-repo: "git://github.com/ocaml-ppx/ppx_import.git"
+dev-repo: "git+https://github.com/ocaml-ppx/ppx_import.git"
 tags: [ "syntax" ]
 
 depends: [