message: Update CHANGELOG.md entry
diff: * For Mono-based development (e.g. Unity) that requires full .NET framework, you need to set `"omnisharp.useGlobalMono": "always"`. The current value of "auto" will remain "never" until Mono [upgrades their bundled MSBuild version](https://github.com/mono/mono/issues/20250).
  * Known limitations with the preview Razor (cshtml) language service to be addressed in a future release:
  * Only ASP.NET Core projects are supported (no support for ASP.NET projects)
  - * Limited support for formatting
  * Error squiggles misaligned for expressions near the start of a new line
  * Emmet based abbreviation expansion is not yet supported (See note in readme for how to enable through your settings.json)
  * There currently is no completion support for package references in csproj files. ([#1156](https://github.com/OmniSharp/omnisharp-vscode/issues/1156))
  * Set meaning of UseGlobalMono "auto" to "never" since Mono 6.12.0 still ships with MSBuild 16.7 (PR: [#4130](https://github.com/OmniSharp/omnisharp-vscode/pull/4130))
  * Ensure that the rename identifier and run code action providers do not apply changes twice (PR: [#4133](https://github.com/OmniSharp/omnisharp-vscode/pull/4133))
  * Do not send file changed events for .cs files (PR: [#4141](https://github.com/OmniSharp/omnisharp-vscode/pull/4141), [#4143](https://github.com/OmniSharp/omnisharp-vscode/pull/4143))
  -* Update Razor to 6.0.0-alpha1.20521.3:
  +* Update Razor to 6.0.0-alpha.1.20529.17:
  * Improvements to HTML colorization for non-C# portions of the document.
  * Bug fix - the `razor.format.enable` option is honored again
  