Make public database as default database
Make public database as default database

This commit will fix the panic when database is not specified.

rickmak/skygear-server,SkygearIO/skygear-server,SkygearIO/skygear-server,rickmak/skygear-server,rickmak/skygear-server,SkygearIO/skygear-server,SkygearIO/skygear-server