Update dependencies

Author: Cito

.travis.yml

@@ -3,7 +3,7 @@ matrix:
   include:
     - name: Code quality tests
       env: TOXENV=black,flake8,mypy,docs,manifest
-      python: 3.8
+      python: 3.9
     - name: Unit tests with Python 3.9
       env: TOXENV=py39
       python: 3.9
@@ -33,7 +33,7 @@ deploy:
   on:
     branch: main
     tags: true
-    python: 3.8
+    python: 3.9
   skip_existing: true
   user: mvanlonden
   password: