title: How to upgrade msbuild to C# 6?
body: <p>I want to use C# 6 in my project (null propagation, other features).</p>
  
  <p>I've installed VS 2015 on my PC and it works brilliantly and builds test code like</p>
  
  <pre><code>var user = new SingleUserModel(); //all model fields are null
  var test = user.User?.Avatar?["blah"];
  </code></pre>
  
  <p>But when I push my project to the repo and CI starts to build it, build fails because of unsupported <code>?</code>.</p>
  
  <p>I've installed VS2015 on CI server too but looke like it doesn't use it.
  What can I do?</p>
  
  <p>CI - CruiseControl .NET
  Builds with <code>C:\Windows\Microsoft.NET\Framework\v4.0.30319\MSBuild.exe</code></p>