Add arm64 support

Dockerfile.dapper

@@ -12,11 +12,12 @@ RUN apt-get update && \
 
 ENV DOCKER_URL_amd64=https://get.docker.com/builds/Linux/x86_64/docker-1.10.3 \
     DOCKER_URL_arm=https://github.com/rancher/docker/releases/download/v1.10.3-ros1/docker-1.10.3_arm \
+    DOCKER_URL_arm64=https://github.com/rancher/docker/releases/download/v1.10.3-ros1/docker-1.10.3_arm64 \
     DOCKER_URL=DOCKER_URL_${ARCH}
 
 RUN wget -O - ${!DOCKER_URL} > /usr/bin/docker && chmod +x /usr/bin/docker
 
-ENV GOLANG_ARCH_amd64=amd64 GOLANG_ARCH_arm=armv6l GOLANG_ARCH=GOLANG_ARCH_${ARCH} \
+ENV GOLANG_ARCH_amd64=amd64 GOLANG_ARCH_arm=armv6l GOLANG_ARCH_arm64=arm64 GOLANG_ARCH=GOLANG_ARCH_${ARCH} \
     GOPATH=/go PATH=/go/bin:/usr/local/go/bin:${PATH} SHELL=/bin/bash
 
 RUN wget -O - https://storage.googleapis.com/golang/go1.12.linux-${!GOLANG_ARCH}.tar.gz | tar -xzf - -C /usr/local