lighttpd: fix sed usage to make the helper not complain

helpers/make-lighttpd

@@ -19,10 +19,11 @@ VERSION=1
 
 . ./config
 
-sed -e 's~Ubuntu\sBug\sTracking\sSystem~upstream bug tracker~g' \
-    -e 's~Ubuntu~Trisquel GNU/Linux~g'                          \
-    -e 's~packages\.ubuntu\.com~packages.trisquel.info~g'       \
-    -i debian/index.html
+HTML_FILE=debian/index.html
+
+sed -i 's~Ubuntu\sBug\sTracking\sSystem~upstream bug tracker~g' $HTML_FILE
+sed -i 's~Ubuntu~Trisquel GNU/Linux~g'                          $HTML_FILE
+sed -i 's~packages\.ubuntu\.com~packages.trisquel.info~g'       $HTML_FILE
 
 changelog "Fix Ubuntu references in the default index.html"