Add package-lock.json which generate by npm
Add package-lock.json which generate by npm

After running tox, generate the package-lock.json
file by npm command.
So that, add it into .gitignore file.

Change-Id: I612a5225963007896b5c18d6cec535d0e09d934a

noironetworks/horizon,NeCTAR-RC/horizon,openstack/horizon,noironetworks/horizon,ChameleonCloud/horizon,noironetworks/horizon,openstack/horizon,noironetworks/horizon,ChameleonCloud/horizon,openstack/horizon,openstack/horizon,NeCTAR-RC/horizon,NeCTAR-RC/horizon,ChameleonCloud/horizon,ChameleonCloud/horizon,NeCTAR-RC/horizon