WinPTY-rs release v0.3.8

Minor winpty-rs that brings compatibility with windows-rs v0.3.9 and fixes some issues when the documentation is being compiled in a non-Windows host

What's Changed

• Update windows requirement from 0.38.0 to 0.39.0 by @dependabot in #40
• Make sure that the docs can be compiled from a non-Windows host machine by @andfoy in #41

Full Changelog: v0.3.7...v0.3.8