changelog for devtools-on-devtools warning fix

CHANGELOG.md

@@ -2,6 +2,10 @@
 All notable changes to `dash` will be documented in this file.
 This project adheres to [Semantic Versioning](http://semver.org/).
 
+## Unreleased
+### Fixed
+- [#969](https://github.com/plotly/dash/pull/969) Fix warnings emitted by react devtools coming from our own devtools components.
+
 ## [1.4.0] - 2019-10-08
 ### Added
 - [#948](https://github.com/plotly/dash/pull/948) Support setting working directory for R apps run using the `dashr` fixture, primarily useful for tests with assets. `dashr.start_server` supports a `cwd` argument to set an explicit working directory, and has smarter defaults when it's omitted: if `app` is a path to an R script, uses the directory of that path; if `app` is a string, uses the directory the test file itself is in.