Bump urllib3 from 1.26.2 to 1.26.19

Bumps [urllib3](https://github.com/urllib3/urllib3) from 1.26.2 to 1.26.19.
- [Release notes](https://github.com/urllib3/urllib3/releases)
- [Changelog](https://github.com/urllib3/urllib3/blob/1.26.19/CHANGES.rst)
- [Commits](urllib3/urllib3@1.26.2...1.26.19)

---
updated-dependencies:
- dependency-name: urllib3
  dependency-type: direct:development
...

Signed-off-by: dependabot[bot] <[email protected]>

requirements-dev.txt

@@ -18,4 +18,4 @@ pytest
 # this shouldn't be necessary, but tox can't seem to find the installed slackclient in
 # tests otherwise
 slackclient==1.2.1
-urllib3==1.26.2
+urllib3==1.26.19