Tag correction.

git-svn-id: http://svn.linuxfromscratch.org/LFS/trunk/BOOK@4657 4aa44e1e-78dd-0310-a6d2-fbcd4c07a689

chapter06/zlib.xml

@@ -50,7 +50,7 @@ configure command below, then remove it afterwards.</para></note>
 
 <screen><userinput>make install</userinput></screen>
 
-<para>Next we will remove the old, <filename>.so</filename> files in
+<para>Next we will remove the old, <filename class="extension">.so</filename> files in
 the <filename class="directory">/lib</filename> directory and relink them
 into <filename class="directory">/usr/lib</filename>.</para>