Fix javadoc errors/warnings

By: Celtic Minstrel <celtic.minstrel.ca@some.place>

paper-api/src/main/java/org/bukkit/entity/LivingEntity.java

@@ -252,6 +252,7 @@ public interface LivingEntity extends Entity {
      * effect of the given {@link PotionEffectType} applied to it.
      *
      * @param type The potion type to check
+     * @return Whether the player has this potion effect active on them.
      */
     public boolean hasPotionEffect(PotionEffectType type);