feat(deps): bump pytz from 2021.1 to 2021.3

Bumps [pytz](https://github.com/stub42/pytz) from 2021.1 to 2021.3.
- [Release notes](https://github.com/stub42/pytz/releases)
- [Commits](stub42/pytz@release_2021.1...release_2021.3)

---
updated-dependencies:
- dependency-name: pytz
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

Signed-off-by: dependabot[bot] <support@github.com>

requirements.txt

@@ -1,5 +1,5 @@
 ConfigArgParse==1.4
-pytz==2021.1
+pytz==2021.3
 isodate==0.6.0
 pylast==4.2.1
 lxml==4.6.3