Bump pip from 9.0.1 to 19.2 in /requirements

Bumps [pip](https://github.com/pypa/pip) from 9.0.1 to 19.2.
- [Release notes](https://github.com/pypa/pip/releases)
- [Changelog](https://github.com/pypa/pip/blob/main/NEWS.rst)
- [Commits](pypa/pip@9.0.1...19.2)

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

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

Author: dependabot[bot]

requirements/pip.txt

@@ -1,3 +1,3 @@
-pip==9.0.1
+pip==19.2
 setuptools==44.1.1
 wheel==0.30.0