Attempt another docker repo

.drone.yml

@@ -4,10 +4,10 @@ name: default
 type: docker
 steps:
   - name: Build
-    image: dotnet/core/sdk:3.1
+    image: mcr.microsoft.com/dotnet/core/sdk:3.1
     commands:
       - dotnet build -c Release
   - name: Tests
-    image: dotnet/core/sdk:3.1
+    image: mcr.microsoft.com/dotnet/core/sdk:3.1
     commands:
       - dotnet test -v n