switch docker build to multiplatform github action

.github/workflows/docker-ci.yml

@@ -0,0 +1,31 @@
+name: docker-ci
+
+on:
+  push:
+    branches:
+      - 'master'
+
+jobs:
+  docker:
+    runs-on: ubuntu-latest
+    steps:
+      -
+        name: Set up QEMU
+        uses: docker/setup-qemu-action@v1
+      -
+        name: Set up Docker Buildx
+        uses: docker/setup-buildx-action@v1
+      -
+        name: Login to DockerHub
+        uses: docker/login-action@v1 
+        with:
+          username: ${{ secrets.DOCKERHUB_USERNAME }}
+          password: ${{ secrets.DOCKERHUB_TOKEN }}
+      -
+        name: Build and push
+        id: docker_build
+        uses: docker/build-push-action@v2
+        with:
+          platforms: linux/amd64,linux/arm64,linux/386,linux/arm/v7
+          push: true
+          tags: ${{secrets.DOCKERHUB_USERNAME}}/dumbproxy:latest