feat: add python 3.9 and 3.10 to ci using focal distribution

Author: Tyskiep99

.travis.yml

@@ -1,13 +1,16 @@
+dist: focal
 language: python
 python:
 - '3.6'
 - '3.7'
 - '3.8'
+- '3.9'
+- '3.10.1'
 install:
 - pip install -r requirements.txt
 - pip install -r dev_requirements.txt --upgrade
 - pip install coveralls
 script:
 - pytest --cov flask_authz
 after_success:
-- coveralls
+- coveralls