add isort to project

.travis.yml

@@ -3,8 +3,8 @@ python:
   - "3.7"
   - "3.8"
 # command to install dependencies
-install: "pip install pytest pytest-black pytest-cov pytest-mypy pytest-pylint pytest-flake8 coveralls"
+install: "pip install pytest pytest-black pytest-cov pylint-isort pytest-mypy pytest-pylint pytest-flake8 coveralls"
 # command to run tests
-script: pytest --black --pylint --pylint-jobs=4 --mypy --cov=pyrad3 --flake8
+script: pytest --black --isort --pylint --pylint-jobs=4 --mypy --flake8 --cov=pyrad3 
 after_success:
   - coveralls