Update dotnetcore.yml

Author: myloveCc

.github/workflows/dotnetcore.yml

@@ -10,13 +10,15 @@ jobs:
   build:
 
     runs-on: ubuntu-latest
-
+    strategy:
+      matrix:
+        dotnet-version: ['3.0', '3.1.x', '5.0.x', '6.0' ]
     steps:
     - uses: actions/checkout@v2
     - name: Setup .NET Core
-      uses: actions/setup-dotnet@v2.1.0
+      uses: actions/setup-dotnet@v1
       with:
-        dotnet-version: 6.0
+        dotnet-version: ${{ matrix.dotnet-version }}
     - name: Install dependencies
       run: dotnet restore
     - name: Build