fix: doc/requirements.txt to reduce vulnerabilities

The following vulnerabilities are fixed by pinning transitive dependencies:
- https://snyk.io/vuln/SNYK-PYTHON-NUMPY-2321964
- https://snyk.io/vuln/SNYK-PYTHON-NUMPY-2321966
- https://snyk.io/vuln/SNYK-PYTHON-NUMPY-2321969
- https://snyk.io/vuln/SNYK-PYTHON-NUMPY-2321970

Author: snyk-bot

doc/requirements.txt

@@ -8,7 +8,7 @@ pandas==1.0.3
 statsmodels==0.11.1
 scipy==1.3.1
 patsy==0.5.1
-numpy==1.19.5
+numpy==1.22.2
 plotly-geo
 python-igraph
 geopandas==0.8.1