Update docker-image.yml - support amd64 too

Author: HarelM

.github/workflows/docker-image.yml

@@ -15,3 +15,4 @@ jobs:
         name: israelhikingmap/elevationwebapi
         username: ${{ secrets.DOCKER_USERNAME }}
         password: ${{ secrets.DOCKER_PASSWORD }}
+        platforms: linux/amd64,linux/arm64