Bump numpy from 1.16.0 to 1.22.0 in /docs/source

Bumps [numpy](https://github.com/numpy/numpy) from 1.16.0 to 1.22.0.
- [Release notes](https://github.com/numpy/numpy/releases)
- [Changelog](https://github.com/numpy/numpy/blob/main/doc/HOWTO_RELEASE.rst)
- [Commits](numpy/numpy@v1.16.0...v1.22.0)

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

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

Author: dependabot[bot]

docs/source/requirements.txt

@@ -1,6 +1,6 @@
 scikit-learn==0.20.2
 scipy==1.2.0
-numpy==1.16.0
+numpy==1.22.0
 numpydoc==0.8.0
 cvxpy
 m2r