Update tox.ini and .gitlab-ci.yml to test formatting updates

.gitlab-ci.yml

@@ -20,6 +20,14 @@ stages:
 before_script:
 - pip install -e .[dev]
 
+linting:
+  image: python:3.6
+  tags:
+  - passoft
+  stage: test
+  script:
+  - flake8 --ignore=F403,F405,F821,F841,W504 ckMseed
+
 python3.6:
   image: python:3.6
   tags:

tox.ini

 [tox]
-envlist = py36, py37, py38
+envlist = py36, py37, py38, flake8
+
+[testenv:flake8]
+basepython = python
+deps = flake8
+commands = flake8 --ignore=F403,F405,F821,F841,W504 ckMseed
 
 [testenv]
 commands = python -m unittest