Update changelog

Author: Jürgen Hasch

CHANGELOG.md

@@ -18,12 +18,14 @@ readthedocs stuff gets all the shiny link goodness. Thanks!
 Unreleased (aka. GitHub master)
 -------------------------------
 
-This is where each new PR to the project should add a summary of its changes,
-which makes it much easier to fill in each release's changelog :)
+0.5.3
+-----
 
 - Replace `template_path` with `extra_template_paths` [#1532](https://github.com/ipython-contrib/jupyter_contrib_nbextensions/pull/1532). Nbconvert 6.0 replaced `template_path` with `extra_template_paths` (see https://nbconvert.readthedocs.io/en/latest/changelog.html#significant-changes). This change in Nbconvert 6.0 causes errors in jupyter_latex_envs and in jupyter_contrib_nbextensions (see [#1529](https://github.com/ipython-contrib/jupyter_contrib_nbextensions/issues/1529).
 - Update `install_requires` list in `setup.py` with 'nbconvert >=6.0' 
 - Drop support for python < 3.6
+- [toc2] fix for disappearing sidebar in static html_toc export [#1548](https://github.com/ipython-contrib/jupyter_contrib_nbextensions/pull/1548)  
+
 
 0.5.1
 -----