Upgrade to newer vscode-json-languageservice

[mickaelistria]

Newer version of VSCode ships a new major of vscode-json-languageservice. To ease mixing both, it would be nice to have yaml-language-server able to work with this new major, otherwise multiple versions of vscode-json-languageservice need to be installed, leading to more disk space usage and more issues in some cases (eg eclipse-wildwebdeveloper/wildwebdeveloper#618 (comment) )

[mickaelistria]

Thanks a lot @evidolob ! Do you have an estimation of what a new release of yaml-language-server is going to take place? Knowing that would help us in deciding when to produce next Wild Web Developer release.

[evidolob]

@mickaelistria Usually we make a release on sprint end. I add milestone to this issue.