Bump pytz from 2020.1 to 2020.4

Bumps [pytz](https://github.com/stub42/pytz) from 2020.1 to 2020.4.
- [Release notes](https://github.com/stub42/pytz/releases)
- [Commits](https://github.com/stub42/pytz/compare/release_2020.1...release_2020.4)

requirements.txt

@@ -26,7 +26,7 @@ pytest-lazy-fixture==0.6.3
 pytest==6.1.1
 python-dateutil==2.8.1
 python-intervals==1.10.0.post1
-pytz==2020.1
+pytz==2020.4
 PyWavelets==1.1.1
 zipp==3.3.0
 wcwidth==0.2.5

sphinx-doc/requirements_sphinx.txt

@@ -41,7 +41,7 @@ pytest==6.1.1
 pytest-lazy-fixture==0.6.3
 python-dateutil==2.8.1
 python-intervals==1.10.0
-pytz==2019.3
+pytz==2020.4
 PyWavelets==1.1.1
 recommonmark==0.6.0
 regex==2020.10.11