Update flake8 requirement from <5 to <7 (#190)

Updates the requirements on [flake8](https://github.com/pycqa/flake8) to permit the latest version.
- [Release notes](https://github.com/pycqa/flake8/releases)
- [Commits](PyCQA/flake8@0.1...6.0.0)

---
updated-dependencies:
- dependency-name: flake8
  dependency-type: direct:development
...

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Author: dependabot[bot]

Pipfile

@@ -19,7 +19,7 @@ redis = "*"
 gevent = "*"
 sure = "*"
 pook = "*"
-flake8 = "<5"
+flake8 = "<7"
 xxhash = "*"
 aiohttp = "*"
 async-timeout = "*"