Update provisioning.md
Update provisioning.md

wrong data type was mentioned in table for esVersion field. I expect to regenerate doc here: http://docs.grafana.org/administration/provisioning/#datasources
This problem was noted by @stefanes a while ago here: https://github.com/grafana/grafana/issues/11126#issuecomment-370799209
grafana/grafana,grafana/grafana,grafana/grafana,grafana/grafana,grafana/grafana,grafana/grafana,grafana/grafana