Update master.yml

Author: darnfish

.github/workflows/master.yml

@@ -11,4 +11,4 @@ jobs:
     steps:
       - name: Checkout
         uses: actions/checkout@v2.0.0
-      - uses: ${ env.GITHUB_REPOSITORY }/.github/actions/docker@master
+      - uses: .github/actions/docker@master