Add decrease to EffChange (#5976)

Author: Fusezion

src/main/java/ch/njol/skript/effects/EffChange.java

@@ -87,7 +87,7 @@ public class EffChange extends Effect {
 			{"remove (all|every) %objects% from %~objects%", ChangeMode.REMOVE_ALL},
 
 			{"(remove|subtract) %objects% from %~objects%", ChangeMode.REMOVE},
-			{"reduce %~objects% by %objects%", ChangeMode.REMOVE},
+			{"(reduce|decrease) %~objects% by %objects%", ChangeMode.REMOVE},
 
 			{"(delete|clear) %~objects%", ChangeMode.DELETE},