Correct broken link for flex, this fixes ticket 1742.

git-svn-id: http://svn.linuxfromscratch.org/LFS/trunk/BOOK@7430 4aa44e1e-78dd-0310-a6d2-fbcd4c07a689

chapter03/packages.xml

@@ -131,7 +131,7 @@
     <varlistentry>
       <term>Flex (&flex-version;) - 672 KB:</term>
       <listitem>
-        <para><ulink url="&sourceforge;lex/"/></para>
+        <para><ulink url="&sourceforge;flex/"/></para>
       </listitem>
     </varlistentry>