fix CI build

.appveyor.yml

@@ -1,6 +1,6 @@
 # To activate, change the Appveyor settings to use `.appveyor.yml`.
 install:
-  - python -m pip install tox
+  - python -m pip install --upgrade tox virtualenv
 
 build: off
 

pytest.ini

@@ -5,3 +5,6 @@ filterwarnings =
     error
     # python3.4 raises this when importing setuptools
     ignore:The value of convert_charrefs will become True in 3.5.*:DeprecationWarning
+    # python3 raises this when importing setuptools
+    ignore:the imp module is deprecated in favour of importlib.*:PendingDeprecationWarning
+    ignore:the imp module is deprecated in favour of importlib.*:DeprecationWarning

src/flake8/checker.py

@@ -435,8 +435,9 @@ class FileChecker(object):
             return plugin["plugin"](**arguments)
         except Exception as all_exc:
             LOG.critical(
-                "Plugin %s raised an unexpected exception", plugin["name"],
-                exc_info=True
+                "Plugin %s raised an unexpected exception",
+                plugin["name"],
+                exc_info=True,
             )
             raise exceptions.PluginExecutionFailed(
                 plugin=plugin, exception=all_exc

tox.ini

@@ -47,6 +47,8 @@ deps =
     flake8
     flake8-colors
     flake8-docstrings>=0.2.7
+    # remove when https://gitlab.com/pycqa/flake8-docstrings/issues/36 is fixed
+    pydocstyle<4
     flake8-import-order>=0.9
     flake8-typing-imports>=1.1
     pep8-naming