[libxslt] Use DocBook URL for tutorial DTD

[Nick Wellnhofer <nwellnhof src gnome org>]

commit 49fbde28440e125aafc12ea18980badd7ed939c7
Author: David King <amigadave amigadave com>
Date:   Thu Jan 27 15:33:17 2022 +0000

    Use DocBook URL for tutorial DTD

 doc/tutorial2/libxslt_pipes.xml | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)
---
diff --git a/doc/tutorial2/libxslt_pipes.xml b/doc/tutorial2/libxslt_pipes.xml
index 9a672a9b..2aaac95f 100644
--- a/doc/tutorial2/libxslt_pipes.xml
+++ b/doc/tutorial2/libxslt_pipes.xml
@@ -1,6 +1,6 @@
 <?xml version="1.0" encoding="iso-8859-2"?>
-<!DOCTYPE article 
-SYSTEM "file:///usr/share/docbook/docbook-xml-4.3/docbookx.dtd">
+<!DOCTYPE article PUBLIC "-//OASIS//DTD DocBook XML V4.3//EN"
+               "http://www.oasis-open.org/docbook/xml/4.3/docbookx.dtd";>
 
 <article id="libxslt">
 <articleinfo>