title: Nuget error during build
body: <p>I grabbed this repo <a href="https://github.com/commandlineparser/commandline.git" rel="nofollow noreferrer">CommandLIneParser</a></p>
  
  <p>and opened it in Visual Studio 2017.  Build fails because Nuget fails.  In the nuget package manager I see messages like this:</p>
  
  <pre><code>Dependency '"CommandLine": {
    "target": "project"
  }' has invalid version specification.
  </code></pre>
  
  <p>What does that mean and how can I resolve it?</p>
  
  <p>Second problem (may be caused by the first). During build I get this error:</p>
  
  <blockquote>
    <p>Error occurred while restoring NuGet packages: Invalid restore input.
    UAP projects must contain exactly one target framework. Input files:
    C:\Users\Jerry\Source\Repos\commandline\tests\CommandLine.Tests\CommandLine.Tests.csproj,
    C:\Users\Jerry\Source\Repos\commandline\tests\CommandLine.Tests\project.json.</p>
  </blockquote>
  
  <p>but both projects do, in fact, target the same framework (.net 4.5, in this case).  So I'm guessing that the error message means something else?</p>
  
  <p>Update: </p>
  
  <p>Now that I'm looking at the two files in the error message, I'm getting a clue:</p>
  
  <p>CommandLine.Tests.csproj has:</p>
  
  <pre><code>&lt;TargetFrameworks&gt;netstandard1.5;net40;net45&lt;/TargetFrameworks&gt;
  </code></pre>
  
  <p>project.json has:</p>
  
  <pre><code>  "testRunner": "xunit",
  
      "frameworks": {
          "netcoreapp1.0": {
              "buildOptions": {
                  "define": [ "PLATFORM_DOTNET", "SKIP_FSHARP" ],
                  "keyFile": "../../CommandLine.snk"
              },
  </code></pre>
  
  <p>So I see the mismatch.  But that just leaves me with the somewhat-rhetorical question:  "How did the last version ever build?"</p>