Px should not hardcode default height (#1990)

* Px should not hardcode default height
* Changelog

Author: nicolaskruchten

Diff for: CHANGELOG.md

@@ -10,7 +10,8 @@ This project adheres to [Semantic Versioning](http://semver.org/).
  for more information
  - The tutorials of the [plotly.py documentation](https://plot.ly/python/) are
    now in the main [plotly.py Github repository](https://github.com/plotly/plotly.py). Contributions in order to improve or extend the documentation are very welcome!
-
+ - `plotly.express` generated plots no longer have a default height of 600 pixels, instead they inherit the default height of regular figures [#1990](https://github.com/plotly/plotly.py/pull/1990). Note that the `height` argument to each `plotly.express` function can be set to 600 to restore the legacy behavior. 
+ 
 ### Fixed
 
  - Fixed a plotly.express input bug when using data frame indices[#1934](https://github.com/plotly/plotly.py/pull/1934)

Diff for: packages/python/plotly/plotly/express/_core.py

@@ -19,7 +19,7 @@ class PxDefaults(object):
     def __init__(self):
         self.template = None
         self.width = None
-        self.height = 600
+        self.height = None
         self.color_discrete_sequence = None
         self.color_continuous_scale = None
         self.symbol_sequence = None