Use py38 in tests

tox.ini

@@ -5,13 +5,13 @@
 skipsdist = True
 setupdir={toxinidir}/src
 envlist =
-    py37
+    py38
     pep8
 
 [testenv]
 usedevelop = True
 basepython =
-    py37: python3.7
+    py38: python3.8
 
 deps = 
     -r{toxinidir}/src//tests/requirements.txt
@@ -23,7 +23,7 @@ commands =
 [testenv:pep8]
 usedevelop = false
 deps = flake8
-basepython = python3.7
+basepython = python3.8
 commands = flake8
 
 [pytest]
@@ -53,4 +53,4 @@ norecursedirs = tests/* .venv/* .tox/* build/ docs/
 ignore = H405,D100,D101,D102,D103,D104,D105,D200,D202,D203,D204,D205,D211,D301,D400,D401,W503
 show-source = True
 max-line-length = 120
-exclude = .tox,.venv*,tests,build,conf.py
+exclude = .tox,env,tests,build,conf.py