RUN apt-get 慢

RUN apt-get is slow, add a line on RUN apt-get XXX of docker:

RUN echo "" > /etc/apt/sources.list
RUN echo "deb http://mirrors.ustc.edu.cn/debian stable main contrib non-free" >> /etc/apt/sources.list
RUN echo "deb-src http://mirrors.ustc.edu.cn/debian stable main contrib non-free" >> /etc/apt/sources.list
RUN echo "deb http://mirrors.ustc.edu.cn/debian stable-proposed-updates main contrib non-free" >> /etc/apt/sources.list
RUN echo "deb-src http://mirrors.ustc.edu.cn/debian stable-proposed-updates main contrib non-free" >> /etc/apt/sources.list