change hostname of postgres service in gitlab testing

.gitlab-ci.yml

@@ -25,7 +25,7 @@ build:
 
 test1:
   variables:
-    DATABASE_URL: "jdbc:postgresql://localhost/docstorage?user=dbuser&password=dbpassword" 
+    DATABASE_URL: "jdbc:postgresql://postgres/docstorage?user=dbuser&password=dbpassword" 
   stage: test
   script:
     - lein test