title: vagrant up: Got different reports about installed GuestAdditions version
body: <p>When doing a <code>vagrant up</code> I get:</p>
  
  <pre><code>Got different reports about installed GuestAdditions version:
  Virtualbox on your host claims:   5.0.28
  VBoxService inside the vm claims: 5.1.18
  Going on, assuming VBoxService is correct...
  </code></pre>
  
  <p>I had a quick search but nothing that resolves this.</p>
  
  <p>It doesn't seem to be impacting anything so just wondered what the best practice is here...</p>