Changing DTD version to meet KDE 4.2

--- ./doc/en/index.docbook
+++ ./doc/en/index.docbook
@@ -1,5 +1,5 @@
 <?xml version="1.0" ?>
-<!DOCTYPE book PUBLIC "-//KDE//DTD DocBook XML V4.1.2-Based Variant V1.1//EN" "dtd/kdex.dtd" [
+<!DOCTYPE book PUBLIC "-//KDE//DTD DocBook XML V4.2-Based Variant V1.1//EN" "dtd/kdex.dtd" [
   <!ENTITY kcollectd "<application>kcollectd 0.8</application>">
   <!ENTITY kappname "&kcollectd;">
   <!ENTITY package "kcollectd">