修改 PreconditionsExt，添加注释。

src/main/java/xyz/zhouxy/plusone/commons/util/EnumUtil.java

@@ -46,7 +46,7 @@ public final class EnumUtil {
     public static <E extends Enum<?>> E valueOf(Class<E> clazz, int ordinal) {
         Preconditions.checkNotNull(clazz, "Clazz must not be null.");
         E[] values = clazz.getEnumConstants();
-        PreconditionsExt.isTrue((ordinal >= 0 && ordinal < values.length),
+        PreconditionsExt.check((ordinal >= 0 && ordinal < values.length),
                 () -> new EnumConstantNotPresentException(clazz, Integer.toString(ordinal)));
         return values[ordinal];
     }