maint: fix THANKS misspellings

* THANKS: Fix recently-introduced misspellings.

THANKS

@@ -536,7 +536,7 @@ Warner Losh		[email protected]
 Warren Dodge		[email protected]
 Wayne Christopher	[email protected]
 Werner Almesberger	[email protected]
-Wichar Minnaard		[email protected]
+Wicher Minnaard		[email protected]
 William Bader		[email protected]
 William J. Eaton	[email protected]
 William Kucharski	[email protected]