Unable to build with NuGet-based SDK

[jeremyVignelles]

Steps to reproduce

Project file

<Project Sdk="MSBuild.Sdk.Extras/1.6.46">
  <PropertyGroup>
    <TargetFrameworks>netstandard2.0</TargetFrameworks>
  </PropertyGroup>
</Project>

Command line

msbuild > build.txt

Expected behavior

The build should complete fine (granted, without files, it won't do much, but still...)

Actual behavior

The build fails with these messages:

Microsoft (R) Build Engine version 15.8.0.0 ( Tue Nov  6 14:11:13 UTC 2018) for Mono
Copyright (C) Microsoft Corporation. All rights reserved.

Build started 11/11/2018 2:31:46 PM.
/data/projects/dotnet/testMsbuild/TestMsbuild.csproj : error : /usr/share/dotnet/sdk/2.1.403/Sdks/MSBuild.Sdk.Extras/Sdk not found. Check that a recent enough .NET Core SDK is installed and/or increase the version specified in global.json.
Project "/data/projects/dotnet/testMsbuild/TestMsbuild.csproj" on node 1 (default targets).
/data/projects/dotnet/testMsbuild/TestMsbuild.csproj : error MSB4236: The SDK 'MSBuild.Sdk.Extras/1.6.46' specified could not be found.
Done Building Project "/data/projects/dotnet/testMsbuild/TestMsbuild.csproj" (default targets) -- FAILED.

Build FAILED.

  /data/projects/dotnet/testMsbuild/TestMsbuild.csproj : error : /usr/share/dotnet/sdk/2.1.403/Sdks/MSBuild.Sdk.Extras/Sdk not found. Check that a recent enough .NET Core SDK is installed and/or increase the version specified in global.json.

"/data/projects/dotnet/testMsbuild/TestMsbuild.csproj" (default target) (1) ->
  /data/projects/dotnet/testMsbuild/TestMsbuild.csproj : error MSB4236: The SDK 'MSBuild.Sdk.Extras/1.6.46' specified could not be found.

    0 Warning(s)
    2 Error(s)

Time Elapsed 00:00:00.16

Environment data

msbuild /version output:

15.8.0.0 Installed with these instructions for 18.04. (version 15.8+xamarinxplat.2018.07.31.22.43-0xamarin6+ubuntu1804b1)

OS info:

Ubuntu MATE 18.10

[jeremyVignelles]

Fixed by #7