Duplicate the copyright message from the source files.

build/SharedVersion.props

@@ -3,7 +3,7 @@
   <PropertyGroup>
     <Product>Avalonia</Product>
     <Version>0.6.2</Version>
-    <Copyright>Copyright 2016 &#169; AvaloniaUI</Copyright>
+    <Copyright>Copyright 2016 &#169; The AvaloniaUI Project</Copyright>
     <PackageLicenseUrl>https://github.com/AvaloniaUI/Avalonia/blob/master/licence.md</PackageLicenseUrl>
     <PackageProjectUrl>https://github.com/AvaloniaUI/Avalonia/</PackageProjectUrl>
     <RepositoryUrl>https://github.com/AvaloniaUI/Avalonia/</RepositoryUrl>