Bump urllib3 from 1.26.6 to 1.26.18 (#219)

Bumps [urllib3](https://github.com/urllib3/urllib3) from 1.26.6 to 1.26.18.
- [Release notes](https://github.com/urllib3/urllib3/releases)
- [Changelog](https://github.com/urllib3/urllib3/blob/main/CHANGES.rst)
- [Commits](urllib3/urllib3@1.26.6...1.26.18)

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

Signed-off-by: dependabot[bot] <[email protected]>
Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

requirements-frozen.txt

@@ -27,6 +27,6 @@ sorl-thumbnail==12.6.3
 sqlparse==0.4.4
 tqdm==4.42.1
 typed-ast==1.4.1
-urllib3==1.26.6
+urllib3==1.26.18
 Whoosh==2.7.4
 wrapt==1.11.2