Add missing constant tag for $flags param of Attribute::__construct()

Author: kocsismate

language/predefined/attribute/construct.xml

@@ -10,7 +10,7 @@
   &reftitle.description;
   <constructorsynopsis role="Attribute">
    <modifier>public</modifier> <methodname>Attribute::__construct</methodname>
-   <methodparam choice="opt"><type>int</type><parameter>flags</parameter><initializer>Attribute::TARGET_ALL</initializer></methodparam>
+   <methodparam choice="opt"><type>int</type><parameter>flags</parameter><initializer><constant>Attribute::TARGET_ALL</constant></initializer></methodparam>
   </constructorsynopsis>
   <para>
    Constructs a new <classname>Attribute</classname> instance.