Dropped dependency on System.Memory for .NET Standard 2.1

Author: MarkCiliaVincenti

ListShuffle/ListShuffle.csproj

@@ -45,7 +45,10 @@
 
 	<ItemGroup>
 		<PackageReference Include="DotNet.ReproducibleBuilds" Version="1.1.1" PrivateAssets="All" />
-		<PackageReference Include="System.Memory" Version="4.5.5" />
 		<PackageReference Include="ThreadSafeRandomizer" Version="1.1.4" />
 	</ItemGroup>
+
+	<ItemGroup Condition="'$(TargetFramework)' == 'netstandard2.0'">
+		<PackageReference Include="System.Memory" Version="4.5.5" />
+	</ItemGroup>
 </Project>