fix code

原先的写法在运行时没有错，但是在读代码的时候，会发现按住ctrl点击`format(((Long) obj))`时，仍会定位到 `String format(final Object obj)`上，给人一种可能会栈溢出的错觉。
@see https://github.com/apache/commons-lang/blob/master/src/main/java/org/apache/commons/lang3/time/FastDatePrinter.java

hutool-core/src/main/java/cn/hutool/core/date/format/FastDatePrinter.java

@@ -299,7 +299,7 @@ public class FastDatePrinter extends AbstractDateBasic implements DatePrinter {
 		} else if (obj instanceof Calendar) {
 			return format((Calendar) obj);
 		} else if (obj instanceof Long) {
-			return format(((Long) obj));
+			return format(((Long) obj).longValue());
 		} else {
 			throw new IllegalArgumentException("Unknown class: " + (obj == null ? "<null>" : obj.getClass().getName()));
 		}