SONARCLOUD-161 use postgresql 9.5 in QA

.cirrus.yml

@@ -101,7 +101,9 @@ qa_task:
     memory: 10Gb
     additional_containers:
     - name: postgres
-      image: postgres:9.3
+      # 9.5 is the version used internally at SonarSource.
+      # The minimal supported version is 9.3 and is tested by nightly QA jobs.
+      image: postgres:9.5
       port: 5432
       cpu: 1
       memory: 1Gb