Fix typo (#202)

Author: tom-konda

reference/exec/functions/proc-open.xml

@@ -242,7 +242,7 @@
   &reftitle.examples;
   <para>
    <example>
-    <title>A <function>proc_open</function> の例</title>
+    <title><function>proc_open</function> の例</title>
     <programlisting role="php">
 <![CDATA[
 <?php