Hover unmarshal fails for singleton MarkedString

[fhs]

The LSP spec allows either MarkedString, []MarkedString, or MarkupContent for Hover.contents. The go-langserver sends a []MarkedString, so there is no issue there. Python-language-server however send a MarkedString and the unmarshal fails with this error:

json: cannot unmarshal string into Go struct field Hover.contents of type []lsp.MarkedString

This is part of a more general issue of how encoding/json package unmarshals slices (issue golang/go#19854).