Remove NetStandard 2.0 (Due Using C# 8.0 above)

Author: HowToDoThis

src/ICSharpCode.SharpZipLib/ICSharpCode.SharpZipLib.csproj

@@ -1,7 +1,7 @@
 <Project Sdk="Microsoft.NET.Sdk">
 
   <PropertyGroup>
-    <TargetFrameworks>netstandard2;netstandard2.1</TargetFrameworks>
+    <TargetFramework>netstandard2.1</TargetFramework>
     <SignAssembly>True</SignAssembly>
     <AssemblyOriginatorKeyFile>../../assets/ICSharpCode.SharpZipLib.snk</AssemblyOriginatorKeyFile>
     <GeneratePackageOnBuild>false</GeneratePackageOnBuild>