chore: Pin flake8 dependency in tox.ini (#417)

Author: lavaleri

tox.ini

@@ -138,11 +138,7 @@ commands = {[testenv:test-upstream-requirements-base]commands}
 [testenv:flake8]
 basepython = python3
 deps =
-    flake8
-    flake8-docstrings>=1.5.0
-    # https://github.com/JBKahn/flake8-print/pull/30
-    flake8-print>=3.1.0
-    flake8-bugbear
+    -rdev_requirements/linter-requirements.txt
 commands =
     flake8 src/aws_encryption_sdk/ setup.py