[PATCH] Fix a typo in chapter 6

[wuzhouhui]

There is only one file (named svnserve.conf) that we are talking about.
Is 'variables' that the author really want to say?

Index: trunk/en/book/ch06-server-configuration.xml
===================================================================
diff --git a/trunk/en/book/ch06-server-configuration.xml b/trunk/en/book/ch06-server-configuration.xml
--- a/trunk/en/book/ch06-server-configuration.xml	(revision 5683)
+++ b/trunk/en/book/ch06-server-configuration.xml	(working copy)
@@ -1049,7 +1049,7 @@ $
         (<literal>[</literal> and <literal>]</literal>), comments
         begin with hashes (<literal>#</literal>), and each section
         contains specific variables that can be set (<literal>variable
-        = value</literal>).  Let's walk through these files and learn
+        = value</literal>).  Let's walk through these variables and learn
         how to use them.</para>
 
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