setup: Configure flake8 extension as a local plugin

We don't want to install this as a system plugin. Now that flake8 3.5.0
is in the wild, we can use this.

Signed-off-by: Stephen Finucane <stephen@that.guru>
Fixes: #4492

1 files changed, 4 insertions, 0 deletions

diff --git a/setup.cfg b/setup.cfg
index c19d0d518..cab6b74d1 100644
--- a/setup.cfg
+++ b/setup.cfg
@@ -34,6 +34,10 @@ max-line-length = 95
 ignore = E116,E241,E251,E741
 exclude = .git,.tox,.venv,tests/*,build/*,doc/_build/*,sphinx/search/*,sphinx/pycode/pgen2/*,doc/ext/example*.py
 
+[flake8:local-plugins]
+extension =
+    X101 = utils.checks:sphinx_has_header
+
 [mypy]
 python_version = 2.7
 show_column_numbers = True