fix grammar in sanctuary documentation

doc/game/Priest.html

@@ -28,7 +28,7 @@ <h2 id='L1'>Level 1</h2>
 amount of damage to it. It has no effect on non-undead.</li>
 <li>Location: (C 1) Returns the party's x-y location in the town or outdoors.</li>
 <li>Sanctuary: (C 1) The target of this spell becomes magically shielded.</li>
-<li>For a time, monsters probably won't be able to attack them. The effects disappears
+<li>For a time, monsters probably won't be able to attack them. The effects disappear
 when the PC attacks someone.</li>
 <li>Symbiosis: (C 3) This spell has the caster absorb the damage taken by another
 character. The higher the caster's level, the less damage the caster takes per health