[POC] Add pyupgrade via pre-commit

new file:   .pre-commit-config.yaml
modified:   tox.ini

.pre-commit-config.yaml

@@ -0,0 +1,11 @@
+repos:
+  - repo: https://github.com/asottile/pyupgrade
+    rev: v2.6.2
+    hooks:
+    - id: pyupgrade
+      args: [--py36-plus]
+
+  - repo: https://github.com/pre-commit/pre-commit-hooks
+    rev: v3.1.0
+    hooks:
+      - id: debug-statements

tox.ini

@@ -7,7 +7,8 @@ envlist =
     py38,
     py39,
     lint,
-    coverage-report
+    pre-commit,
+    coverage-report,
 
 [testenv]
 coverage_run = {env:WIN_COV:coverage run}
@@ -95,3 +96,8 @@ deps =
 commands =
     - isort --check-only --recursive {toxinidir}/src setup.py
     flake8 src docs setup.py
+
+[testenv:pre-commit]
+skip_install = true
+deps = pre-commit
+commands = pre-commit run --all-files --show-diff-on-failure