add netcoreapp3.1 target

Author: neuecc

src/ConsoleAppFramework/ConsoleAppFramework.csproj

@@ -1,13 +1,11 @@
 <Project Sdk="Microsoft.NET.Sdk">
     <PropertyGroup>
-        <TargetFrameworks>netstandard2.0;net5.0</TargetFrameworks>
+        <TargetFrameworks>netstandard2.0;netcoreapp3.1;net5.0</TargetFrameworks>
         <LangVersion>8.0</LangVersion>
         <Nullable>enable</Nullable>
         <SignAssembly>true</SignAssembly>
         <AssemblyOriginatorKeyFile>release.snk</AssemblyOriginatorKeyFile>
         <GenerateDocumentationFile>true</GenerateDocumentationFile>
-        <!-- Version is passed from CircleCI -->
-        <!--<Version>1</Version>-->
 
         <!-- NuGet -->
         <PackageId>ConsoleAppFramework</PackageId>
@@ -27,4 +25,4 @@
     <ItemGroup>
         <None Include="Icon.png" Pack="true" PackagePath="/" />
     </ItemGroup>
-</Project>
+</Project>