Fix Travis pipeline

.pre-commit-config.yaml

@@ -1,9 +1,9 @@
 repos:
   - repo: https://github.com/psf/black
-    rev: ''
+    rev: '22.10.0'
     hooks:
       - id: black
   - repo: https://gitlab.com/pycqa/flake8
-    rev: ''
+    rev: '3.9.2'
     hooks:
       - id: flake8

.travis.yml

@@ -17,6 +17,7 @@ dist: xenial
 os: linux
 
 install:
+- if [[ $TRAVIS_PYTHON_VERSION == 3.7 ]]; then pip install -U importlib_metadata; fi
 - pip install coverage coveralls
 - test ! "$PRE_COMMIT" || pip install pre-commit
 - pip install "mypy>=0.782"