fix dotnet core version

NwNsgProject/NwNsgProject.csproj

@@ -1,6 +1,6 @@
 <Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
-    <TargetFramework>netcoreapp3.0</TargetFramework>
+    <TargetFramework>netcoreapp3.1</TargetFramework>
     <AzureFunctionsVersion>v3</AzureFunctionsVersion>
   </PropertyGroup>
   <ItemGroup>