Make dune subst only available in dev

Author: xvw

CHANGES.md

@@ -1,5 +1,3 @@
-## dev (Unreleased)
-
 ## v0.1.0 (August 2021)
 
 - First release (`v0.1.0`) by [**@d-plaindoux**](https://github.com/d-plaindoux), [**@gr-im**](https://github.com/gr-im), [**@xhtmlboi**](https://github.com/xhtmlboi) and [**@xvw**](https://github.com/xvw)

preface.opam

@@ -15,15 +15,15 @@ dev-repo: "git+https://github.com/xvw/preface.git"
 bug-reports: "https://github.com/xvw/preface/issues"
 
 build: [
-  [ "dune" "subst" ]
+  [ "dune" "subst" ] {dev}
   [ "dune" "build" "-p" name "-j" jobs ]
   [ "dune" "runtest" "-p" name ] {with-test}
   [ "dune" "build" "@doc" "-p" name ] {with-doc}
 ]
 
 depends: [
   "ocaml" { >= "4.08.0" }
-  "dune" { >= "2.7.1" }
+  "dune" { >= "2.8.0" }
   "either"
   "alcotest" {with-test}
   "qcheck-core" {with-test}