Update

ftplugin/dune.vim

@@ -0,0 +1,14 @@
+if !exists('g:polyglot_disabled') || index(g:polyglot_disabled, 'ocaml') == -1
+
+if exists("b:did_ftplugin")
+  finish
+endif
+let b:did_ftplugin=1
+
+set lisp
+
+" Comment string
+setl commentstring=;\ %s
+setl comments=:;
+
+endif