Update twine to 1.9.1

[pyup-bot]

There's a new version of twine available.
You are currently using 1.8.1. I have updated it to 1.9.1

These links might come in handy: PyPI | Changelog | Repo

Changelog

1.9.1

• Blacklist known bad versions of Requests. See also 🐛253

1.9.0

• Twine will now resolve passwords using the
  keyring <https://pypi.org/projects/keyring>_ if available.
  Module can be required with the keyring extra.

• Twine will use hashlib.blake2b on Python 3.6+ instead of using pyblake2
  for Blake2 hashes 256 bit hashes.

• Twine sends less information about the user's system in the User-Agent
  string. See also 🐛229

• Fix --skip-existing when used to upload a package for the first time.
  See also 🐛220

• Fix precedence of --repository-url over --repository. See also
  🐛206

Got merge conflicts? Close this PR and delete the branch. I'll create a new PR for you.

Happy merging! 🤖