example in `session()` breaks because target file name has changed

[luisDVA]

Hi!
The example for session() is breaking because the target image url in the example (https://hadley.nz/hadley-wickham.jpg) does not exist any more so a 404 is thrown. This makes the tests fail.

 s <- session("http://hadley.nz")
 s |>
   session_jump_to("hadley-wickham.jpg") |>
   session_jump_to("/") |>
   session_history()

Looking at the hadleyzn website repo, the image filename is just 'hadley.jpg'