Add expression switch to job update sed statement

Local testing passed, but when run in the gate, script execution failed
on the sed expression not being preceded by '-e'.

Change-Id: I02545e1f976f220f197556bdfa6e6225d9bd8d36
Signed-off-by: Sean McGinnis <sean.mcginnis@gmail.com>

roles/copy-release-tools-scripts/files/release-tools/add_master_python3_jobs.sh

@@ -48,7 +48,7 @@ git checkout master
 fnames=$(find . -type f -path '*zuul.d/*'; find . -type f -name '*zuul.yaml')
 for fname in $fnames; do
     echo "Checking ${fname}"
-    sed -i \
+    sed -i -e \
         "s/openstack-python3-${OLDSERIES}-jobs/openstack-python3-${SERIES}-jobs/g" \
         $fname
 done