chore(deps): bump mypy-extensions in /dev_requirements (#393)

Bumps [mypy-extensions](https://github.com/python/mypy_extensions) from 0.4.3 to 1.0.0.
- [Commits](python/mypy_extensions@0.4.3...1.0.0)

---
updated-dependencies:
- dependency-name: mypy-extensions
  dependency-type: direct:production
  update-type: version-update:semver-major
...

Signed-off-by: dependabot[bot] <[email protected]>
Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

Author: dependabot[bot]

dev_requirements/coverage-requirements.txt

@@ -1,6 +1,6 @@
 coverage==4.5.4
 mypy==0.971
-mypy-extensions==0.4.3
+mypy-extensions==1.0.0
 typing==3.7.4.3
 types-setuptools==63.2.2
 types-six==1.16.21