fix typo in docker build

Author: ernado

.github/workflows/dockerimage.yml

@@ -8,4 +8,4 @@ jobs:
     steps:
       - uses: actions/checkout@v1
       - name: Build the Docker image
-        run: docker build . --file Dockerfile --tag golangci-lint-action-:$(date +%s)
+        run: docker build . --file Dockerfile --tag golangci-lint-action:$(date +%s)