add containers and remove jane streets stdio

src/dune

@@ -1,6 +1,6 @@
 (library
  (name aoc)
- (libraries stdio re dune-site)
+ (libraries re containers dune-site)
  (preprocess (pps ppx_regexp)))
 
 (install

src/utils.ml

@@ -1,3 +1,5 @@
+open Containers
+
 let lines_of_input day =
   let base_path =
     match Inputs.Sites.inputs with
@@ -5,5 +7,5 @@ let lines_of_input day =
     | _ -> failwith "cant find path containing inputs"
   in
   let path = Printf.sprintf "%s/day%d.tt" base_path day in
-  Stdio.In_channel.(with_file path ~f:input_lines)
+  IO.(with_in path read_lines_l)
 ;;