Security upgrade nginx from 1.19.7-alpine to 1.20.1-alpine

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 severity	500	Out-of-bounds Read
SNYK-ALPINE313-APKTOOLS-1533754	No Known Exploit
critical severity	500	Double Free
SNYK-ALPINE313-CURL-1585246	No Known Exploit
critical severity	500	Double Free
SNYK-ALPINE313-CURL-1585246	No Known Exploit
critical severity	500	Buffer Overflow
SNYK-ALPINE313-OPENSSL-1569448	No Known Exploit
critical severity	500	Buffer Overflow
SNYK-ALPINE313-OPENSSL-1569448	No Known Exploit

nginx-wsgi-flask/nginx/Dockerfile

@@ -1,4 +1,4 @@
-FROM nginx:1.19.7-alpine
+FROM nginx:1.20.1-alpine
 
 # Add bash for boot cmd
 RUN apk add bash