Target netstandard2.0 and net8.0

Resolves #133

Author: Jericho

Source/HttpMultipartParser/HttpMultipartParser.csproj

@@ -1,7 +1,7 @@
 <Project Sdk="Microsoft.NET.Sdk">
 
   <PropertyGroup>
-    <TargetFrameworks>net48;netstandard2.1</TargetFrameworks>
+    <TargetFrameworks>netstandard2.0;net8.0</TargetFrameworks>
     <LangVersion>preview</LangVersion>
     <PlatformTarget>anycpu</PlatformTarget>
     <GenerateDocumentationFile>true</GenerateDocumentationFile>
@@ -46,12 +46,7 @@
     <PackageReference Include="System.Buffers" Version="4.6.1" />
   </ItemGroup>
 
-  <ItemGroup Condition=" $(TargetFramework.StartsWith('net4')) ">
-    <Reference Include="Microsoft.CSharp" />
-    <Reference Include="System" />
-  </ItemGroup>
-
-  <ItemGroup Condition=" $(TargetFramework.StartsWith('netstandard')) ">
+  <ItemGroup Condition=" '$(TargetFramework)' == 'netstandard2.0' ">
     <PackageReference Include="Microsoft.CSharp" Version="4.7.0" />
   </ItemGroup>