Modify project file to support 3.1 SDK

Co-authored-by: Pranav K <prkrishn@hotmail.com>

src/Microsoft.AspNetCore.Components.WebAssembly.DebugProxy/Microsoft.AspNetCore.Components.WebAssembly.DebugProxy.csproj

@@ -1,4 +1,5 @@
-<Project Sdk="Microsoft.NET.Sdk">
+<Project Sdk="Microsoft.NET.Sdk.Web">
+
 
   <PropertyGroup>
     <TargetFramework>netcoreapp2.1</TargetFramework>