chap7/stripping: when refering $LFS as an envar, use <envar> instead of <filename>

git-svn-id: http://svn.linuxfromscratch.org/LFS/trunk/BOOK@11968 4aa44e1e-78dd-0310-a6d2-fbcd4c07a689

chapter07/stripping.xml

@@ -155,7 +155,7 @@ tar -cJpf $HOME/lfs-temp-tools-&versiond;.tar.xz .</userinput></screen>
       Since the sources are located under 
       <filename class="directory">$LFS</filename>, they are included in the
       backup archive as well, so they do not need to be downloaded again. After
-      checking that <filename class="directory">$LFS</filename> is set properly,
+      checking that <envar>$LFS</envar> is set properly,
       restore the backup by executing the following commands:
     </para>