Update container image

Author: liufengyun

Diff for: .github/workflows/ci.yaml

@@ -21,7 +21,7 @@ jobs:
       - name: Test
         uses: liufengyun/actions@v2
         with:
-          container: lampepfl/dotty-windows:2020-10-02
+          container: lampepfl/dotty-windows:2020-10-06
           command: sbt test
 
   test_bootstrapped-windows:
@@ -34,7 +34,7 @@ jobs:
       - name: Test
         uses: liufengyun/actions@v2
         with:
-          container: lampepfl/dotty-windows:2020-10-02
+          container: lampepfl/dotty-windows:2020-10-06
           command: sbt dotty-bootstrapped/test
 
       # - name: Scala.js Test