add postgres image to circleci config

.circleci/config.yml

@@ -19,16 +19,17 @@ jobs:
     docker:
       # specify the version you desire here
       - image: circleci/node:12.6
+        environment:
+          DATABASE_URL: postgresql://root@localhost/circle_test
           
-      # Specify service dependencies here if necessary
-      # CircleCI maintains a library of pre-built images
-      # documented at https://circleci.com/docs/2.0/circleci-images/
-      # - image: circleci/mongo:3.4.4
+    # Service container image
+      - image: circleci/postgres:9.6.5-alpine-ram
 
     working_directory: ~/node-go
 
     steps:
       - checkout
+      - run: sudo apt-get install postgresql-client-9.6
 
       # Download and cache dependencies
       - restore_cache: