Update containers and NGINX Plus version (#63)

Go to 1.16
golangci-lint to 1.38
NGINX Plus to R23

Author: lucacome

Makefile

@@ -1,12 +1,12 @@
-NGINX_PLUS_VERSION=22-1
+NGINX_PLUS_VERSION=23-1
 NGINX_IMAGE=nginxplus:$(NGINX_PLUS_VERSION)
 DOCKER_NETWORK?=test
 DOCKER_NETWORK_ALIAS=nginx-plus-test
 DOCKER_NGINX_PLUS?=nginx-plus
 DOCKER_NGINX_PLUS_HELPER?=nginx-plus-helper
 
-GOLANG_CONTAINER=golang:1.15
-GOLANGCI_CONTAINER=golangci/golangci-lint:v1.29-alpine
+GOLANG_CONTAINER=golang:1.16
+GOLANGCI_CONTAINER=golangci/golangci-lint:v1.38-alpine
 
 export TEST_API_ENDPOINT=http://$(DOCKER_NGINX_PLUS):8080/api
 export TEST_API_ENDPOINT_OF_HELPER=http://$(DOCKER_NGINX_PLUS_HELPER):8080/api