ci: run tox with -e argument for current python version

Author: mmlb

.drone.yml

@@ -19,4 +19,4 @@ pipeline:
     commands:
       - apt update -y && apt install -y pandoc
       - pip install pypandoc tox
-      - tox
+      - tox -e py$(echo ${PYTHON_VERSION} | sed 's|\.||')

.travis.yml

@@ -12,4 +12,4 @@ python:
 sudo: false
 
 install: pip install pypandoc tox
-script: tox
+script: tox -e py$(echo "$TRAVIS_PYTHON_VERSION" | sed 's|\.||')