Depend on ASP.NET 2.1 packages for netstandard2.0 package

Lowered referenced package versions because the 2.1 versions are
supported by Microsoft, while the 2.2 versions are not.

Fixes #993

src/SoapCore/SoapCore.csproj

@@ -29,10 +29,10 @@
 
 	<ItemGroup Condition="$(TargetFramework) == 'netstandard2.0' OR $(TargetFramework) == 'netstandard2.1'">
 		<PackageReference Include="Newtonsoft.Json" Version="13.0.1" />
-		<PackageReference Include="Microsoft.AspNetCore.Http" Version="2.2.0" />
-		<PackageReference Include="Microsoft.AspNetCore.Mvc.Core" Version="2.2.5" />
-		<PackageReference Include="Microsoft.Extensions.DependencyInjection.Abstractions" Version="2.2.0" />
-		<PackageReference Include="Microsoft.Extensions.Logging.Abstractions" Version="2.2.0" />
+		<PackageReference Include="Microsoft.AspNetCore.Http" Version="2.1.34" />
+		<PackageReference Include="Microsoft.AspNetCore.Mvc.Core" Version="2.1.38" />
+		<PackageReference Include="Microsoft.Extensions.DependencyInjection.Abstractions" Version="2.1.1" />
+		<PackageReference Include="Microsoft.Extensions.Logging.Abstractions" Version="2.1.1" />
 		<PackageReference Include="System.IO.Pipelines" Version="4.7.0" />
 		<PackageReference Include="System.CodeDom" Version="4.7.0" />
 	</ItemGroup>
@@ -59,7 +59,7 @@
 	</ItemGroup>
 
 	<ItemGroup>
-		<PackageReference Include="Microsoft.AspNetCore.Mvc.Abstractions" Version="2.2.0" />
+		<PackageReference Include="Microsoft.AspNetCore.Mvc.Abstractions" Version="2.1.38" />
 		<PackageReference Include="System.ServiceModel.Http" Version="4.8.1" />
 		<PackageReference Include="StyleCop.Analyzers" Version="1.1.118">
 			<PrivateAssets>all</PrivateAssets>