Bump pip from 19.3.1 to 21.1

Bumps [pip](https://github.com/pypa/pip) from 19.3.1 to 21.1.
- [Release notes](https://github.com/pypa/pip/releases)
- [Changelog](https://github.com/pypa/pip/blob/main/NEWS.rst)
- [Commits](pypa/pip@19.3.1...21.1)

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

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

Author: dependabot[bot]

requirements.txt

@@ -10,7 +10,7 @@ networkx==2.4
 numpy==1.17.4  
 opencv-contrib-python==4.1.1.26
 Pillow==8.1.1   
-pip==19.3.1  
+pip==21.1  
 pyparsing==2.4.5   
 python-dateutil==2.8.1   
 PyWavelets==1.1.1