Added explicit Microsoft.Extensions.Configuration.Abstractions for all targets (#590)

Author: snakefoot

src/NLog.Extensions.Logging/NLog.Extensions.Logging.csproj

@@ -77,6 +77,7 @@ NLog 5 release post: https://nlog-project.org/2021/08/25/nlog-5-0-preview1-ready
   </ItemGroup>
   <ItemGroup Condition=" '$(TargetFramework)' == 'net461' ">
     <PackageReference Include="Microsoft.Extensions.Logging" Version="2.1.0" />
+    <PackageReference Include="Microsoft.Extensions.Configuration.Abstractions" Version="2.1.0" />
     <Reference Include="System" />
     <Reference Include="Microsoft.CSharp" />
   </ItemGroup>
@@ -90,9 +91,11 @@ NLog 5 release post: https://nlog-project.org/2021/08/25/nlog-5-0-preview1-ready
   </ItemGroup>
   <ItemGroup Condition=" '$(TargetFramework)' == 'netstandard2.0' ">
     <PackageReference Include="Microsoft.Extensions.Logging" Version="2.1.0" />
+    <PackageReference Include="Microsoft.Extensions.Configuration.Abstractions" Version="2.1.0" />
   </ItemGroup>
   <ItemGroup Condition=" '$(TargetFramework)' == 'netcoreapp3.1' ">
     <PackageReference Include="Microsoft.Extensions.Logging" Version="3.1.0" />
+    <PackageReference Include="Microsoft.Extensions.Configuration.Abstractions" Version="3.1.0" />
   </ItemGroup>
   <ItemGroup Condition=" '$(TargetFramework)' == 'net5.0' ">
     <PackageReference Include="Microsoft.Extensions.Logging" Version="5.0.0" />