Fix typo in language/functions.xml (#4692)

Author: msamesch

language/functions.xml

@@ -282,7 +282,8 @@ echo $str;    // outputs 'This is a string, and something extra.'
      </example>
     </para>
     <para>
-     It is an error to pass a constant expression as argument to parameter that expects to be passed by reference.
+     It is an error to pass a constant expression as an argument to a parameter
+     that expects to be passed by reference.
     </para>
    </sect2>
    <sect2 xml:id="functions.arguments.default">