fix: get arm64 verson of buildx for arm64 image (#8)

Author: fpiesche

docker/Dockerfile.arm64

@@ -15,7 +15,7 @@ ENV DOCKER_HOST=unix:///var/run/docker.sock
 
 RUN apk --update add --virtual .build-deps curl && \
     mkdir -p /usr/lib/docker/cli-plugins/ && \
-    curl -SsL -o /usr/lib/docker/cli-plugins/docker-buildx "https://github.com/docker/buildx/releases/download/v${BUILDX_VERSION}/buildx-v${BUILDX_VERSION}.linux-amd64" && \
+    curl -SsL -o /usr/lib/docker/cli-plugins/docker-buildx "https://github.com/docker/buildx/releases/download/v${BUILDX_VERSION}/buildx-v${BUILDX_VERSION}.linux-arm64" && \
     chmod 755 /usr/lib/docker/cli-plugins/docker-buildx && \
     apk del .build-deps && \
     rm -rf /var/cache/apk/* && \