Pillar repository moved

I'm the author and package maintainer of pillar and I've just moved its
repository to a dedicated team on github.

Old location:
https://github.com/DamienCassou/pillar-mode

New location:
https://github.com/pillar-markup/pillar-mode
Merge pull request #1703 from DamienCassou/pillar-changed-repository

Pillar repository moved