Update comments-since-last-visit.php

[jnz31]

set cookie path, so the cookie is accessible from everywhere and not only saved to the individual post page.

[mindctrl]

@jnz31 thanks for the PR. What problem is this solving for you?

[jnz31]

in my special case i needed the cookie also on the archive pages, so when you pass the cookie-domain, it is only one cookie with an array of all the visited posts and their timestamp. in your case you also created the array, but an individual cookie for each page, only accessible in there..