THRIFT-4990 Switch to .NET core 3.0
Client: netstsd
Patch: Jens Geyer

This closes #1909
diff --git a/tutorial/netstd/Interfaces/Interfaces.csproj b/tutorial/netstd/Interfaces/Interfaces.csproj
index 4ebeb4f..2d8a440 100644
--- a/tutorial/netstd/Interfaces/Interfaces.csproj
+++ b/tutorial/netstd/Interfaces/Interfaces.csproj
@@ -19,7 +19,7 @@
   -->
 
   <PropertyGroup>
-    <TargetFramework>netstandard2.0</TargetFramework>
+    <TargetFramework>netstandard2.1</TargetFramework>
     <AssemblyName>Interfaces</AssemblyName>
     <PackageId>Interfaces</PackageId>
     <GenerateAssemblyConfigurationAttribute>false</GenerateAssemblyConfigurationAttribute>