Update pyserial to 3.4

[pyup-bot]

There's a new version of pyserial available.
You are currently using 3.3. I have updated it to 3.4

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

Changelog

3.4

---

Improvements:

• miniterm: suspend function (temporarily release port, :kbd:Ctrl-T s)
• [240] context manager automatically opens port on __enter__
• [141] list_ports: add interface number to location string
• [225] protocol_socket: Retry if BlockingIOError occurs in
  reset_input_buffer.

Bugfixes:

• [153] list_ports: option to include symlinked devices
• [237] list_ports: workaround for special characters in port names

Bugfixes (posix):

• allow calling cancel functions w/o error if port is closed
• [220] protocol_socket: sync error handling with posix version
• [227] posix: ignore more blocking errors and EINTR, timeout only
  applies to blocking I/O
• [228] fix: port_publisher typo

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

Happy merging! 🤖