我输入这个命令后，就出来这么一个报错

invalid argument "hello_nginx." for t: Error parsing reference: "hello_ng

inx." is not a valid repository/tag: invalid reference formatSee 'docker build --help'.

FROM ubuntu
MAINTAINER xbf
RUN sed -i 's/archive.ubuntu.com/mirrrosl.ustc.edu.cn/g' /etc/apt/sources
.listRUN apt-get update
RUN apt-get install -y nginx
COPY index.html /var/www/html
ENTRYPOINT ["/usr/sbin/nginx","-g","daemon off:"]
EXPOSE 80

我的dockerfile里的内容，和视频里的一样