Merge pull request msgpack#361 from thompson-tomo/chore/#359_AddMoreTFM

msgpack#359 add net core 3.1 & net 6

Author: yfakariya

src/MsgPack/MsgPack.csproj

@@ -4,7 +4,7 @@
     <ProjectGuid>{5BCEC32E-990E-4DE5-945F-BD27326A7418}</ProjectGuid>
     <OutputType>Library</OutputType>
     <AssemblyName>MsgPack</AssemblyName>
-    <TargetFrameworks>net46;net35;net45;netstandard1.1;netstandard1.3;netstandard2.0;MonoAndroid10;Xamarin.iOS10;</TargetFrameworks>
+    <TargetFrameworks>net46;net35;net45;netstandard1.1;netstandard1.3;netstandard2.0;MonoAndroid10;Xamarin.iOS10;netcoreapp3.1;net6.0</TargetFrameworks>
     <AllowUnsafeBlocks>True</AllowUnsafeBlocks>
     <CodeAnalysisRuleSet>AllRules.ruleset</CodeAnalysisRuleSet>
     <NuspecFile>$(SolutionDir)/msgpack.nuspec</NuspecFile>
@@ -16,7 +16,7 @@
   <PropertyGroup Condition="'$(Configuration)' != 'Release'">
     <OutputPath>bin\$(Configuration)\</OutputPath>
   </PropertyGroup>
-  <ItemGroup Condition="'$(TargetFramework)' != 'uap10.0' and '$(TargetFramework)' != 'netstandard1.1' and '$(TargetFramework)' != 'netstandard1.3' and '$(TargetFramework)' != 'netstandard2.0'">
+  <ItemGroup Condition="'$(TargetFramework)' == 'net35' or '$(TargetFramework)'== 'net45' or '$(TargetFramework)' == 'net46'">
     <Reference Include="System" />
     <Reference Include="System.Core" />
     <Reference Include="System.Numerics" Condition="'$(TargetFramework)' != 'net35'" />