Type error into examples

Hello,

Just my first step with Minttea. Very good idea to be inspired by Elm and powered by OCaml.

dune --version 
3.13.1

ocaml --version
The OCaml toplevel, version 5.1.1

➜  progress git:(main) ✗ dune build
Entering directory '/Users/nicolas.muller/projects/minttea/minttea'
File "minttea/renderer.ml", line 112, characters 36-54:
112 |     Riot.Timer.send_interval ~every:(fps_to_float fps) (self ()) Tick
                                          ^^^^^^^^^^^^^^^^^^
Error: This expression has type int64 but an expression was expected of type
         float
File "minttea/program.ml", line 47, characters 54-59:
47 |       let _ = Timer.send_after (self ()) (Timer ref) ~after |> Result.get_ok in
                                                           ^^^^^
Error: This expression has type int64 but an expression was expected of type
         `float`

Thanks a lot, Nicolas