Bump pip from 8.1.2 to 19.2

Bumps [pip](https://github.com/pypa/pip) from 8.1.2 to 19.2.
- [Release notes](https://github.com/pypa/pip/releases)
- [Changelog](https://github.com/pypa/pip/blob/main/NEWS.rst)
- [Commits](https://github.com/pypa/pip/compare/8.1.2...19.2)

---
updated-dependencies:
- dependency-name: pip
  dependency-type: direct:development
...
Signed-off-by: Ndependabot[bot] <support@github.com>

requirements_dev.txt

-pip==8.1.2
+pip==19.2
 bumpversion==0.5.3
 wheel==0.29.0
 watchdog==0.8.3