Update clipboard-win to 4.2.1

[stevanmilic]

By updating the clipboard-win we resolve the issue #9.

Also some of the code has been simplified, since new clipboard-win
version has simplified API.

[stevanmilic]

@equalsraf I've made some improvements that resolves the #9 issue, can you please check the code?

[SamSaffron]

Confirming this fixed #9 for me 🎊 🎊 🎊

Thank you @stevanmilic !

[equalsraf]

I am seeing a test failure for this where the clipboard is not set

https://ci.appveyor.com/project/equalsraf/win32yank/builds/42380293/job/36qim4mhletcn4ob

[elevin72]

I am seeing a test failure for this where the clipboard is not set

https://ci.appveyor.com/project/equalsraf/win32yank/builds/42380293/job/36qim4mhletcn4ob

Here's an odd question. In actual use is it possible to copy an empty string? I understand that the test isn't passing. My understanding is that if you give set_clipboard() an empty string it just won't actually do the set. (See https://github.com/DoumanAsh/clipboard-win/blob/02a16b5dfc92cf7f8897c4aaa4e8e56fab883326/src/raw.rs#L281)
But where in actual use cases is it possible to copy an empty string?

[equalsraf]

Closing, merged #16