bump minimal OCaml version to 4.13

.github/workflows/main.yml

@@ -16,8 +16,7 @@ jobs:
         os:
             - ubuntu-latest
         ocaml-compiler:
-            - '4.08'
-            - '4.14'
+            - '4.13'
             - '5.2'
 
     runs-on: ${{ matrix.os }}

dune-project

@@ -16,7 +16,7 @@
  (name moonpool)
  (synopsis "Pools of threads supported by a pool of domains")
  (depends
-  (ocaml (>= 4.08))
+  (ocaml (>= 4.13))
   dune
   (either (>= 1.0))
   (trace :with-test)

moonpool.opam

@@ -9,7 +9,7 @@ tags: ["thread" "pool" "domain" "futures" "fork-join"]
 homepage: "https://github.com/c-cube/moonpool"
 bug-reports: "https://github.com/c-cube/moonpool/issues"
 depends: [
-  "ocaml" {>= "4.08"}
+  "ocaml" {>= "4.13"}
   "dune" {>= "3.0"}
   "either" {>= "1.0"}
   "trace" {with-test}