Security upgrade nginx from 1.19.7-alpine to 1.20.1-alpine

[cloudgeek7]

Changes included in this PR

• nginx-wsgi-flask/nginx/Dockerfile

We recommend upgrading to nginx:1.20.1-alpine, as this image has only 0 known vulnerabilities. To do this, merge this pull request, then verify your application still works as expected.

Some of the most important vulnerabilities in your base image include:

Severity	Priority Score / 1000	Issue	Exploit Maturity
Critical	500	Out-of-bounds ReadSNYK-ALPINE313-APKTOOLS-1533754	No Known Exploit
Critical	500	Double FreeSNYK-ALPINE313-CURL-1585246	No Known Exploit
Critical	500	Double FreeSNYK-ALPINE313-CURL-1585246	No Known Exploit
Critical	500	Buffer OverflowSNYK-ALPINE313-OPENSSL-1569448	No Known Exploit
Critical	500	Buffer OverflowSNYK-ALPINE313-OPENSSL-1569448	No Known Exploit