Update changelog with config file PR

CHANGELOG.md

 ## v0.12.0 [unreleased]
 
 ### Features
+- [#948](https://github.com/influxdata/telegraf/pull/948): Cleanup config file and make default package version include all plugins (but commented).
 - [#927](https://github.com/influxdata/telegraf/pull/927): Adds parsing of tags to the statsd input when using DataDog's dogstatsd extension
 - [#863](https://github.com/influxdata/telegraf/pull/863): AMQP output: allow external auth. Thanks @ekini!
 - [#707](https://github.com/influxdata/telegraf/pull/707): Improved prometheus plugin. Thanks @titilambert!