MLBEDSW-3367 Update pre-commit flake8 version

Update the version of flake8 used in pre-commit to facilitate
adding mypy to pre-commit.

Signed-off-by: Jonas Ohlsson <jonas.ohlsson@arm.com>
Change-Id: I457dec87b77487ca6f14ff4a679c4cc927b272b0
diff --git a/.pre-commit-config.yaml b/.pre-commit-config.yaml
index 17d3877..8e976b6 100644
--- a/.pre-commit-config.yaml
+++ b/.pre-commit-config.yaml
@@ -13,7 +13,7 @@
         args: [--line-length=120]
 
 -   repo: https://gitlab.com/pycqa/flake8
-    rev: 3.7.9
+    rev: 4.0.1
     hooks:
     -   id: flake8
         args: [--max-line-length=120, --extend-ignore=E203]