Bug 1679056 - Update to flake8 3.8.4.r=sylvestre

PR can be found here:
https://github.com/sylvestre/gecko-dev/pull/165

./mach lint -l flake8

Differential Revision: https://phabricator.services.mozilla.com/D97895

tools/lint/python/flake8_requirements.txt

@@ -1,6 +1,6 @@
-flake8==3.8.3 \
-    --hash=sha256:15e351d19611c887e482fb960eae4d44845013cc142d42896e9862f775d8cf5c \
-    --hash=sha256:f04b9fcbac03b0a3e58c0ab3a0ecc462e023a9faf046d57794184028123aa208
+flake8==3.8.4 \
+    --hash=sha256:749dbbd6bfd0cf1318af27bf97a14e28e5ff548ef8e5b1566ccfb25a11e7c839 \
+    --hash=sha256:aadae8761ec651813c24be05c6f7b4680857ef6afaae4651a4eccaef97ce6c3b
 mccabe==0.6.1 \
     --hash=sha256:ab8a6258860da4b6677da4bd2fe5dc2c659cff31b3ee4f7f5d64e79735b80d42 \
     --hash=sha256:dd8d182285a0fe56bace7f45b5e7d1a6ebcbf524e8f3bd87eb0f125271b8831f