App center API uses deprecated APIs

[sam-mckay]

The App center API makes use of WWW which is deprecated in 2018 and in projects using "warnings as errors" this results in compile errors

The SDK should be updated to UnityWebRequest
This issue applies to
AppCenterEditorHttp.cs
EditorCoroutine.cs

I've worked around this issue for now using #pragma but this should be fixed properly

[maestersid]

@sam-mckay thanks for the heads up, ill have the team look into getting this updated.