`workspace/publishDiagnostics` doesn't pass back version information to client

[Dylmay]

Currently the Python lsp server doesn't pass information about the version of a document that linting was ran on.

This could be a minor improvement for some clients which can drop diagnostics based on out-of-date versions, stopping incorrect diagnostics from being shown

See #565

[ccordoba12]

It'd be nice to have this here, thanks for suggesting and implementing it.