Fix docker build failed, use -f for Dockerfile location

Author: martinussuherman

.github/workflows/snyk-docker-amd64.yml

@@ -15,7 +15,7 @@ jobs:
     - uses: actions/checkout@v2
 
     - name: Build amd64 Docker image
-      run: docker build -t martinussuherman/alpine-code-server:amd64 amd64
+      run: docker build -t martinussuherman/alpine-code-server:amd64 -f amd64/Dockerfile .
 
     - name: Run Snyk to check Docker image for vulnerabilities
       # Snyk can be used to break the build when it detects vulnerabilities.