Update _index.md
Update _index.md

removed the '-' in time series.
influxdata/docs.influxdata.com,influxdb/docs.influxdata.com,influxdb/docs.influxdata.com,influxdata/docs.influxdata.com,influxdata/docs.influxdata.com,influxdb/docs.influxdata.com,influxdata/docs.influxdata.com,influxdata/docs.influxdata.com