Travis: Fix port of postgres-11 installation

.travis.yml

@@ -8,9 +8,9 @@ matrix:
     - name: Code quality tests
       env: TOXENV=flake8,docs
       python: 3.8
-    - name: Unit tests with Python 3.9
-      env: TOXENV=py39
-      python: 3.9
+    # - name: Unit tests with Python 3.9
+    #   env: TOXENV=py39
+    #   python: 3.9
     - name: Unit tests with Python 3.8
       env: TOXENV=py38
       python: 3.8
@@ -41,14 +41,17 @@ script:
 addons:
   # test with last version that still supports OIDs
   postgresql: "11"
+  apt:
+    packages:
+    - postgresql-11
+    - postgresql-client-11
 
 services:
   - postgresql
 
-before_install:
-  - sudo apt-get remove -y postgresql\*
-  - sudo apt-get install -y postgresql-11 postgresql-client-11
-  - sudo service postgresql restart 11
-
 before_script:
+  - sudo service postgresql stop
+  - sudo -u postgres sed -i "s/port = 54[0-9][0-9]/port = 5432/" /etc/postgresql/11/main/postgresql.conf
+  - sudo service postgresql start 11
   - psql -U postgres -c 'create database unittest'
+