Corrected text for ch.5 flex installation

git-svn-id: http://svn.linuxfromscratch.org/LFS/trunk/BOOK@3609 4aa44e1e-78dd-0310-a6d2-fbcd4c07a689

chapter05/flex.xml

@@ -25,7 +25,7 @@
 </sect2>
 
 <sect2 role="installation">
-<title>Installation of Bison</title>
+<title>Installation of Flex</title>
 
 <para>Flex contains several known bugs. Fix these with the following patch:</para>