title: The 'Version' attribute is not declared in nuspec file
body: <p>When I try to pack a .net core solution using VSTS, I get <code>The 'Version' attribute is not declared</code> error. My nuspec file looks like this:</p>
  
  <pre><code>&lt;?xml version="1.0" encoding="utf-8"?&gt;
  &lt;package xmlns="http://schemas.microsoft.com/packaging/2010/07/nuspec.xsd"&gt;
    &lt;metadata minClientVersion="3.3.0"&gt;
      &lt;id&gt;YYY.AspNetCore.CustomMapper&lt;/id&gt;
      &lt;version&gt;0.0.1&lt;/version&gt;
      &lt;authors&gt;build@YYYYYY.com&lt;/authors&gt;
      &lt;owners&gt;YYY YYY&lt;/owners&gt;
      &lt;requireLicenseAcceptance&gt;false&lt;/requireLicenseAcceptance&gt;
      &lt;description&gt;YYY.AspNetCore&lt;/description&gt;
      &lt;tags&gt;YYY&lt;/tags&gt;
      &lt;contentFiles&gt;
          &lt;files include="wwwroot\**" buildAction="EmbeddedResource" copyToOutput="true" /&gt;
          &lt;files include="Areas\CustomMapper\readme.txt" buildAction="EmbeddedResource" copyToOutput="true" /&gt;
      &lt;/contentFiles&gt;
      &lt;dependencies&gt;
      &lt;group&gt;
          &lt;dependency id="EntityFramework" Version="6.1.0" /&gt;
          &lt;dependency id="Microsoft.AspNetCore" Version="1.1.0" /&gt;
          &lt;dependency id="Microsoft.AspNetCore.Mvc" version="1.1.0" /&gt;
          &lt;dependency id="Microsoft.AspNetCore.StaticFiles" version="1.1.0" /&gt;
          &lt;dependency id="Microsoft.Extensions.Logging.Debug" version="1.1.0" /&gt;
          &lt;dependency id="YYY.Web.AspNetCore" version="1.0.1" /&gt;
          &lt;dependency id="SimpleInjector.Integration.AspNetCore" version="4.0.10" /&gt;
          &lt;dependency id="SimpleInjector.Integration.AspNetCore.Mvc" version="4.0.10" /&gt;
      &lt;/group&gt;
    &lt;/dependencies&gt;
    &lt;/metadata&gt;
    &lt;files&gt;
      &lt;file src="wwwroot\**" target="content\wwwroot" /&gt;
      &lt;file src="Areas\CustomMapper\readme.txt" target="" /&gt;
      &lt;file src="bin\Release\net452\win7-x86\YYY.CustomMapper.dll" target="lib\net452" /&gt;
      &lt;file src="bin\Release\net452\win7-x86\YYY.CustomMapper.Data.dll" target="lib\net452" /&gt;
      &lt;file src="bin\Release\net452\win7-x86\YYY.CustomMapper.Provider.dll" target="lib\net452" /&gt;
      &lt;file src="bin\Release\net452\win7-x86\YYY.CustomMapper.Services.dll" target="lib\net452" /&gt;
      &lt;file src="bin\Release\net452\win7-x86\YYY.CustomMapper.WebApi.dll" target="lib\net452" /&gt;
      &lt;file src="bin\Release\net452\win7-x86\YYY.CustomMapper.Backend.WebApi.dll" target="lib\net452" /&gt;
      &lt;file src="bin\Release\net452\win7-x86\YYY.CustomMapper.Provider.Common.dll" target="lib\net452" /&gt;
      &lt;file src="bin\Release\net452\win7-x86\YYY.AspNetCore.CustomMapper.dll" target="lib\net452" /&gt;
    &lt;/files&gt;
  &lt;/package&gt;
  </code></pre>
  
  <p>Can anyone please help me why this error is happening?</p>