Use released EF 6.3 version

Tasteful · Tasteful · commit fa47a4928102 · 2019-10-22T14:22:14.000+02:00
diff --git a/Directory.Build.props b/Directory.Build.props
@@ -13,7 +13,7 @@
   </PropertyGroup>
 
   <PropertyGroup Condition=" '$(TargetFramework)' == 'netstandard2.1' or '$(TargetFramework)' == 'netcoreapp3.0' ">
-    <EFVersion>6.3.0-preview7-*</EFVersion>
+    <EFVersion>6.3.0</EFVersion>
   </PropertyGroup>
 
 </Project>
