Fix addons mailing list string

[kimden]

This is not correct English (same goes for karts and arenas):

CrystalDaEevee has uploaded a new revision for tracks 'Clash-o-8' clash-o-8
skindoormimiz has uploaded a new tracks 'Warpseye' warpseye

Seems like generated around include/Addon.class.php:1962