CHANGELOG: mention removal of deprecated "IF NOT EXISTS" InfluxDB condition

Author: Stephen Gutekanst

CHANGELOG.md

@@ -8,6 +8,7 @@
   - [#157](https://github.com/sourcegraph/appdash/pull/157) Added proper point-batching support to InfluxDBStore.
   - [#157](https://github.com/sourcegraph/appdash/pull/157) Changed `ChunkedCollector.FlushTimeout` default from 50ms to 2s.
   - [#158](https://github.com/sourcegraph/appdash/pull/158) Made InfluxDBStore use Continuous Queries so the Dashboard is very responsive.
+  - [#159](https://github.com/sourcegraph/appdash/pull/159) InfluxDBStore no longer uses the deprecated `IF NOT EXISTS` condition when creating the DB.
 - Apr 15, 2016 - **Breaking Changes!**
   - [#136](https://github.com/sourcegraph/appdash/pull/136) Users must now call `Recorder.Finish` when finished recording, or else data    will not be collected.
   - [#136](https://github.com/sourcegraph/appdash/pull/136) AggregateStore is removed in favor of InfluxDBStore, which is also embeddable, and is generally faster and more reliable. Refer to the [cmd/webapp-influxdb](https://github.com/sourcegraph/appdash/blob/master/examples/cmd/webapp-influxdb/main.go#L50) for further information on how to migrate to `InfluxDBStore`, or [read more about why this change was made](https://github.com/sourcegraph/appdash/issues/137).