我正在尝试在Docker容器中安装New Relic的系统监控，但apt-key add -失败no valid OpenPGP data found。

有完整的Dockerfile：

FROM ubuntu
MAINTAINER Matej Koubik

RUN echo deb http://apt.newrelic.com/debian/ newrelic non-free >> /etc/apt/sources.list.d/newrelic.list
RUN wget -O- https://download.newrelic.com/548C16BF.gpg | apt-key add -
RUN apt-get update
RUN apt-get install newrelic-sysmond
RUN nrsysmond-config --set license_key=...
RUN /etc/init.d/newrelic-sysmond start