module: adopt poetry dependency manager

.travis.yml

@@ -8,21 +8,10 @@ python:
 - "3.7"
 - "3.8"
 
-jobs:
-  fast_finish: true
-  allow_failures:
-  - python: "3.4"
-  - python: "3.5"
-  - python: "3.7"
-  - python: "3.8"
-
-env:
-- PIPENV_VERBOSITY=-1
-
 install:
-- pip install --upgrade pipenv
-- pipenv install --dev
+- pip install poetry
+- poetry install
 
 script:
-- pylint veml6070
-- pytest
+- poetry run pylint veml6070
+- poetry run pytest