message: Update changelog for 1.13.1
diff: * There currently is no completion support for package references in csproj files. ([#1156](https://github.com/OmniSharp/omnisharp-vscode/issues/1156))
  * As an alternative, consider installing the [MSBuild Project Tools](https://marketplace.visualstudio.com/items?itemName=tintoy.msbuild-project-tools) extension by @tintoy.
  +## 1.13.1 (November 13, 2017)
  +
  +* Addressed problem with Sdk-style projects not being loaded properly in certain cases. ([#1846](https://github.com/OmniSharp/omnisharp-vscode/issues/1846), [#1849](https://github.com/OmniSharp/omnisharp-vscode/issues/1849), PR: [omnisharp-roslyn#1021](https://github.com/OmniSharp/omnisharp-roslyn/pull/1021))
  +* Fixed issue with discovering MSBuild under Mono even when it is missing. ([omnisharp-roslyn#1011](https://github.com/OmniSharp/omnisharp-roslyn/issues/1011), PR: [omnisharp-roslyn#1016](https://github.com/OmniSharp/omnisharp-roslyn/pull/1016))
  +* Fixed issue to not use Visual Studio 2017 MSBuild if it is from VS 2017 RTM. ([omnisharp-roslyn#1014](https://github.com/OmniSharp/omnisharp-roslyn/issues/1014), PR: [omnisharp-roslyn#1016](https://github.com/OmniSharp/omnisharp-roslyn/pull/1016))
  +
  ## 1.13.0 (November 7, 2017)
  #### Cake
  