Reduces vulnerabilities in nginx and postgres containers

This change updates the NGINX and postgres container images
used by the Google Marketplace app to reduct the number of
vulnerabilities in the imagers used.

Addresses Issue #33

Makefile

@@ -37,9 +37,9 @@ endif
 
 APP_DEPLOYER_IMAGE ?= $(REGISTRY_PREFIX)/deployer:$(TAG)
 CONJUR_IMAGE ?= $(REGISTRY)/$(PREFIX):$(TAG)
-POSTGRES_SOURCE_IMAGE ?= postgres:10.1
+POSTGRES_SOURCE_IMAGE ?= postgres:9.4
 POSTGRES_IMAGE ?= $(REGISTRY_PREFIX)/postgres:$(TAG)
-NGINX_SOURCE_IMAGE ?= nginx:1.15
+NGINX_SOURCE_IMAGE ?= nginx:1.17
 NGINX_IMAGE ?= $(REGISTRY_PREFIX)/nginx:$(TAG)
 DOCKERFILE ?= deployer/Dockerfile