Correctd some typo's

util.mli

@@ -144,7 +144,7 @@ val node_error : Types.node -> string -> unit
 (** Print a warning message for a node. Calls prerr_loc_msg. *)
 val node_warning : Types.node -> string -> unit
 
-(** {2 String utitities} *)
+(** {2 String utilities} *)
 
 (** [repeat s n] returns a new string of [n] times [s]. *)
 val repeat : string -> int -> string
@@ -153,7 +153,7 @@ val repeat : string -> int -> string
     characters long. *)
 val expand : int -> string -> string
 
-(** {2 List utitities} *)
+(** {2 List utilities} *)
 
 (** [optmap f opt] maps [f] to the list value of [opt] if [opt] exists, and
     [None] otherwise. *)