THANKS: remove incorrect apostrophe

'user' is the adjective describing the 'community'

Close #8518
Signed-off-by: Rémi Denis-Courmont <remi@remlab.net>

THANKS

@@ -90,7 +90,7 @@ Laurent Dupuy, who made a €540 donation
 The French company Cybervia (Actech) gave €2000 to pay for webserver hosting
 Dennis Perov - Hardware donation
 
-...the following active members of our user's community:
+...the following active members of our user community:
 
 Alan Wright
 David J LaBarre "DJ"