Update dotnetcore.yml

Author: Aux

.github/workflows/dotnetcore.yml

@@ -12,6 +12,6 @@ jobs:
     - name: Setup .NET Core
       uses: actions/setup-dotnet@v1
       with:
-        dotnet-version: 3.0.101
+        dotnet-version: 3.1.300-preview-015048
     - name: Build with dotnet
       run: dotnet build --configuration Release