Cookies should include the `SameSite` attribute

[marinbernard-pep06]

Hi,

Recent Firefox versions are throwing a warning about the extension cookie missing the SameSite attribute.

On the following line:

redmine_dark/assets/javascripts/dark.js

Line 5 in 2fcbc05

document.cookie = cname + "=" + cvalue + ";" + expires + ";path=/";

Please add + ";samesite=strict"

Thanks,