Move the 'Release Notes' inside the separate 'Changelog' tab

[darkred]

Currently the 'Release Notes' for every version of the extension is listed inside the 'Details' tab of the Extensions view (Ctrl+Shift+X):

Screenshot

They should show up inside the separate 'Changelog' tab, as in e.g. the 'ESLint' extension:

Screenshot

But, for this extension there's currently no 'Changelog' tab, as seen in the 1st screenshot..

 
The extra "Changelog" tab was feature added in VSCode v1.6 (see these two PRs here). Based on the former PR, a separate changelog.md is required -- but, there is a separate https://github.com/xojs/vscode-linter-xo/blob/master/CHANGELOG.md file already ! (otherwise it should supposedly take changelog from remote).

So, I can't tell why this is not working..

Thank you

PS. Related, fixed issue: microsoft/vscode-eslint#204

[spence-s]

done edbf830