Update upgrading.md
Update upgrading.md

generalized the "setup" of the version numbers.
influxdata/docs.influxdata.com,influxdata/docs.influxdata.com,influxdata/docs.influxdata.com,influxdata/docs.influxdata.com,influxdb/docs.influxdata.com,influxdb/docs.influxdata.com,influxdb/docs.influxdata.com,influxdata/docs.influxdata.com