fix: docker-examples/v5/reverse_proxy/nginx/relative_path/nginx/Docke…

…rfile to reduce vulnerabilities (verdaccio#2371)

The following vulnerabilities are fixed with an upgrade:
- https://snyk.io/vuln/SNYK-ALPINE314-CURL-1533447
- https://snyk.io/vuln/SNYK-ALPINE314-CURL-1533452
- https://snyk.io/vuln/SNYK-ALPINE314-CURL-1533458
- https://snyk.io/vuln/SNYK-ALPINE314-CURL-1533461
- https://snyk.io/vuln/SNYK-ALPINE314-CURL-1533461

docker-examples/v5/reverse_proxy/nginx/relative_path/nginx/Dockerfile

@@ -1,2 +1,2 @@
-FROM nginx:mainline-alpine
+FROM nginx:1.21-alpine
 COPY nginx/default.conf /etc/nginx/conf.d/default.conf