Fix typo on recent commit.

git-svn-id: http://svn.linuxfromscratch.org/LFS/trunk/BOOK@11105 4aa44e1e-78dd-0310-a6d2-fbcd4c07a689

chapter07/systemd-custom.xml

@@ -191,7 +191,7 @@ EOF</userinput></screen>
       <listitem>
         <para>
           <emphasis>Enable process lingering for only needed users</emphasis>:
-          normal users have permission to enabling process lingering
+          normal users have permission to enable process lingering
           with the command <command>loginctl enable-linger</command> for their
           own user. System administrators can use the same command with a
           <parameter>user</parameter> argument to enable for a user. That user