Use proper naming convention for boolean methods.

By: Travis Watkins <amaranth@ubuntu.com>

paper-server/src/main/java/org/bukkit/craftbukkit/entity/CraftLivingEntity.java

@@ -379,7 +379,7 @@ public class CraftLivingEntity extends CraftEntity implements LivingEntity {
         getHandle().setCustomNameVisible(flag);
     }
 
-    public boolean getCustomNameVisible() {
+    public boolean isCustomNameVisible() {
         return getHandle().getCustomNameVisible();
     }
 }