Bump urllib3 from 1.25.7 to 1.26.5

Bumps [urllib3](https://github.com/urllib3/urllib3) from 1.25.7 to 1.26.5.
- [Release notes](https://github.com/urllib3/urllib3/releases)
- [Changelog](https://github.com/urllib3/urllib3/blob/main/CHANGES.rst)
- [Commits](https://github.com/urllib3/urllib3/compare/1.25.7...1.26.5)

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

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

requirements.txt

@@ -11,6 +11,6 @@ mpmath==1.1.0
 numpy==1.17.4
 requests==2.22.0
 sympy==1.4
-urllib3==1.25.7
+urllib3==1.26.5
 Werkzeug==0.16.0
 matplotlib==3.1.2