Fix compile error

spectec/src/backend-prose/render.mli

@@ -11,7 +11,7 @@ val env : Config.config -> string list -> string list -> Backend_latex.Render.en
 (* Generators *)
 
 val render_expr : env -> expr -> string
-val render_instr : Al.Ast.(env -> id -> int ref -> int -> instr -> string)
+val render_instr : env -> Al.Ast.id -> int ref -> int -> Al.Ast.instr -> string
 val render_stmt : env -> int -> stmt -> string
 val render_def : env -> def -> string
 val render_prose : env -> prose -> string