[Snyk] Fix for 9 vulnerabilities

[snyk-bot]

Snyk has created this PR to fix one or more vulnerable packages in the `pip` dependencies of this project.

Changes included in this PR

• Changes to the following files to upgrade the vulnerable dependencies to a fixed version:
  • docs/requirements.txt

⚠️ Warning

``` Sphinx 1.8.6 has requirement docutils<0.18,>=0.11, but you have docutils 0.18.1. sphinx-rtd-theme 0.5.2 has requirement docutils<0.17, but you have docutils 0.18.1. ```

Vulnerabilities that will be fixed

By pinning:

Severity	Issue	Upgrade	Breaking Change	Exploit Maturity
	Incorrect Access Control SNYK-PYTHON-DASK-1767103	dask: 2.30.0 -> 2021.10.0	No	No Known Exploit
	NULL Pointer Dereference SNYK-PYTHON-NUMPY-2321964	numpy: 1.21.3 -> 1.22.2	No	Proof of Concept
	Buffer Overflow SNYK-PYTHON-NUMPY-2321966	numpy: 1.21.3 -> 1.22.2	No	No Known Exploit
	Denial of Service (DoS) SNYK-PYTHON-NUMPY-2321970	numpy: 1.21.3 -> 1.22.2	No	Proof of Concept
	Denial of Service (DoS) SNYK-PYTHON-PILLOW-2329135	pillow: 8.4.0 -> 9.0.1	No	No Known Exploit
	Arbitrary Code Execution SNYK-PYTHON-PILLOW-2331901	pillow: 8.4.0 -> 9.0.1	No	No Known Exploit
	Buffer Over-read SNYK-PYTHON-PILLOW-2331905	pillow: 8.4.0 -> 9.0.1	No	No Known Exploit
	Improper Initialization SNYK-PYTHON-PILLOW-2331907	pillow: 8.4.0 -> 9.0.1	No	No Known Exploit
	Improper Input Validation SNYK-PYTHON-PILLOW-2397241	pillow: 8.4.0 -> 9.0.1	No	No Known Exploit

Some vulnerabilities couldn't be fully fixed and so Snyk will still find them when the project is tested again. This may be because the vulnerability existed within more than one direct dependency, but not all of the effected dependencies could be upgraded.

Check the changes in this PR to ensure they won't cause issues with your project.

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