阶乘优化

hutool-core/src/test/java/cn/hutool/core/util/NumberUtilTest.java

@@ -249,7 +249,7 @@ public class NumberUtilTest {
 		Assert.assertEquals(120, factorial);
 		factorial = NumberUtil.factorial(5, 1);
 		Assert.assertEquals(120, factorial);
-
+		Assert.assertEquals(5, NumberUtil.factorial(5, 4));
 		Assert.assertEquals(2432902008176640000L, NumberUtil.factorial(20, 0));
 	}