Update CHANGELOG.md

Author: jackparmer

CHANGELOG.md

@@ -2,6 +2,10 @@
 All notable changes to this project will be documented in this file.
 This project adheres to [Semantic Versioning](http://semver.org/).
 
+## [2.3.4] - 2017-12-11
+### Fixed
+- Merged [pull request](https://github.com/plotly/plotly.py/commit/a226e07393c158e01c34c050aaf492da9d77679a) that fixes `GraphWidget` for IPython > v6
+
 ## [2.2.3] - 2017-12-04
 ### Added
 -`column_width` and `row_width` parameters for `plotly.tools.make_subplots`. Call `help(plotly.tools.make_subplots)` for documentation.