title: Problem on Unity 2020 and Firebase (Unable to resolve reference 'UnityEditor.iOS.Extensions.Xcode')
body: <p>I upgrade my app for Android on Unity 2019.12 to 2020.1. With Unity 2019, Firebase work fine. But with Unity 2020, i have 2 errors. I not use IOS, just Android. How to resolve this ?
  Thanks.</p>
  <pre><code>Assembly 'Assets/Firebase/Editor/Firebase.Editor.dll' will not be loaded due to errors:
  Unable to resolve reference 'UnityEditor.iOS.Extensions.Xcode'. Is the assembly missing or incompatible with the current platform?
  Reference validation can be disabled in the Plugin Inspector.
  
  Assembly 'Assets/PlayServicesResolver/Editor/Google.IOSResolver_v1.2.135.0.dll' will not be loaded due to errors:
  Unable to resolve reference 'UnityEditor.iOS.Extensions.Xcode'. Is the assembly missing or incompatible with the current platform?
  Reference validation can be disabled in the Plugin Inspector.
  </code></pre>