Update opam file for dune port

Signed-off-by: Stephen Sherratt <stephen@sherra.tt>

ptime.opam

@@ -22,17 +22,14 @@ under the ISC license.
 
 Home page: <http://erratique.ch/software/ptime>"""
 maintainer: "Daniel Bünzli <daniel.buenzl i@erratique.ch>"
-authors: "The ptime programmers"
+authors: ["The ptime programmers"]
 license: "ISC"
 tags: ["time" "posix" "system" "org:erratique"]
-homepage: "https://erratique.ch/software/ptime"
-doc: "https://erratique.ch/software/ptime/doc/"
+homepage: "https://github.com/dune-universe/ptime"
 bug-reports: "https://github.com/dbuenzli/ptime/issues"
 depends: [
+  "dune"
   "ocaml" {>= "4.08.0"}
-  "ocamlfind" {build}
-  "ocamlbuild" {build & != "0.9.0"}
-  "topkg" {build & >= "1.0.3"}
 ]
-build: ["ocaml" "pkg/pkg.ml" "build" "--dev-pkg" "%{dev}%"]
-dev-repo: "git+https://erratique.ch/repos/ptime.git"
+build: [ "dune" "build" "-p" name "-j" jobs "@install" "@runtest" {with-test} ]
+dev-repo: "git+https://github.com/dune-universe/ptime.git"