Update enum.md

Haskell uses data. OCaml and F# do use type, and SML does use datatype. There is no "data" in any ML that I know.

src/types/enum.md

@@ -16,7 +16,7 @@ Enum types cannot be denoted *structurally* as types, but must be denoted by
 named reference to an [`enum` item].
 
 [^enumtype]: The `enum` type is analogous to a `data` constructor declaration in
-             ML, or a *pick ADT* in Limbo.
+             Haskell, or a *pick ADT* in Limbo.
 
 [`enum` item]: ../items/enumerations.md
 [struct expression]: ../expressions/struct-expr.md