Update .travis.yml

.travis.yml

@@ -1,16 +1,19 @@
+dist: focal
 language: python
 python:
   - 3.6
   - 3.7
   - 3.8
   - 3.9
 before_install:
+  - sudo apt-get install libgnutls28-dev
   - python --version
   - pip install -U pip
-  - pip install -U pytest
   - pip install codecov
-install:
-  - pip install -r lambda/requirements.txt # install package + test dependencies
-script: pytest # run tests
+install: "pip install -r lambda/requirements.txt"
+script:
+  - flake8 --ignore=E501,W503 lambda
+  - coverage run lambda/lambda_function.py
 after_success:
-  - codecov # submit coverage
+  - bash <(curl -s https://codecov.io/bash)
+  - codecov