Bump pip from 19.2 to 21.1

Bumps [pip](https://github.com/pypa/pip) from 19.2 to 21.1.
- [Release notes](https://github.com/pypa/pip/releases)
- [Changelog](https://github.com/pypa/pip/blob/main/NEWS.rst)
- [Commits](pypa/pip@19.2...21.1)

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

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

Author: dependabot[bot]

requirements.txt

@@ -24,7 +24,7 @@ pandas==0.23.4
 patsy==0.5.0
 pexpect==4.6.0
 pickleshare==0.7.5
-pip==19.2
+pip==21.1
 ptyprocess==0.6.0
 pyOpenSSL==18.0.0
 pycparser==2.19