period as last character in username breaks activation link

[ilikewordpress]

Many browsers and mail clients are converting text-URLs to clickable links.

If a user chooses an username with a period at the end, the activation link in the mail could be incorrect, because the mail client thinks, the period is a punctuation character.

See this (non-working) URL for an example:
​https://www.domain.de/wp-login.php?action=rp&key=XXXXXX&user=ballspieler96.

The period at the end is part of the username but not part of the URL.

Fix:
Don't use the username as last parameter. Instead use a defined parameter, which won't have periods as value (i.e. 2action" or "key")