Fix modification-check.sh (#4091)

* Run build.py

* Restore letsencrypt-auto after running build

* Remove temp_dir before exiting

* add missing $

tests/modification-check.sh

@@ -46,6 +46,7 @@ cd ${SCRIPT_PATH}/../
 cp letsencrypt-auto-source/letsencrypt-auto ${temp_dir}/original-lea
 python letsencrypt-auto-source/build.py
 cp letsencrypt-auto-source/letsencrypt-auto ${temp_dir}/build-lea
+cp ${temp_dir}/original-lea letsencrypt-auto-source/letsencrypt-auto
 
 cd $temp_dir
 
@@ -60,8 +61,8 @@ else
 build.py."
 fi
 
+rm -rf $temp_dir
+
 if $FLAG ; then
 	exit 1
 fi
-
-rm -rf temp_dir