Update time_precision to use 'ms'

InfluxDB has deprecated the use of 'm' for `time_precision`. We need to use 'ms' now.
```
[WARN] (github.com/influxdb/influxdb/api/http.TimePrecisionFromString:280) time_precision=m will be disabled in future release, use time_precision=ms instead
```
Merge pull request #1 from justindowning/patch-1

Update time_precision to use 'ms'