Fix TA-Lib URL as per #4462

Author: philip

reference/trader/book.xml

@@ -18,7 +18,7 @@
   Some trader functions provide different results depending of the &quot;starting point&quot; of the data being involved. This is often referred as a function having memories. An example of such function is the Exponential Moving Average. It is possible to control the unstable period (the amount of data to strip off) using <link xmlns="http://docbook.org/ns/docbook" linkend="function.trader-set-unstable-period">trader_set_unstable_period()</link> function.
   </para>
   <para>
-   Extended documentation about indicators, formulas and implementations in other programming languages can be found under <link xlink:href="http://tadoc.org/">tadoc.org</link>.
+   Extended documentation about indicators, formulas and implementations in other programming languages can be found under <link xlink:href="&url.trader.lib;">&url.trader.lib;</link>.
   </para>
  </preface>