final touch to CI

.gitlab-ci.yml

-image: python:3.6.5-jessie
-
-services:
-  - postgres:9.6.8
-
 testing:
   stage: test
+  image: python:3.6.5-jessie
+  services:
+    - postgres:9.6.8
   script:
     - export ENV=development
     - export DATABASE_URL=postgres://postgres:@postgres:5432/python-test-app
@@ -22,6 +20,7 @@ testing:
 
 flake8:
   stage: test
+  image: python:3.6.5-jessie
   script:
     - pip install flake8
     - flake8
@@ -41,8 +40,8 @@ pages:
     paths:
       - public
     expire_in: 1 month
-  # only: 
-  #   - master
+  only: 
+    - master
   tags:
     - docker