Fix default cost in constants.xml

Author: nielsdos

reference/password/constants.xml

@@ -43,7 +43,7 @@
         page.
        </para>
        <para>
-        If omitted, a default value of <literal>10</literal> will be used. This is a good
+        If omitted, a default value of <literal>12</literal> will be used. This is a good
         baseline cost, but you may want to consider increasing it depending on your hardware.
        </para>
       </listitem>