Use .NET SDK 3.1.x

Author: jcansdale

.github/workflows/generate.yml

@@ -16,7 +16,7 @@ jobs:
     - name: Setup .NET Core
       uses: actions/setup-dotnet@v1
       with:
-        dotnet-version: 1.1.2
+        dotnet-version: 3.1.x
 
     - name: Install dependencies
       run: dotnet restore