Fix version of sdk

Author: macsux

.github/workflows/dotnet.yaml

@@ -15,10 +15,10 @@ jobs:
         uses: actions/setup-dotnet@v1
         with:
           dotnet-version: 2.1.202
-      - name: Setup dotnet runtime 2.1.17
+      - name: Setup dotnet runtime 2.1.0
         uses: actions/setup-dotnet@v1
         with:
-          dotnet-version: 2.1.805
+          dotnet-version: 2.1.300
       - name: Setup dotnet SDK 3.1
         uses: actions/setup-dotnet@v1
         with: