给树莓派换一个靠谱的源

亲测好用，下载速度快

sudo nano /etc/apt/sources.list

deb 
http://mirrors.tuna.tsinghua.edu.cn/raspbian/raspbian/ jessie main non-free$

deb-src http://mirrors.tuna.tsinghua.edu.cn/raspbian/raspbian/ jessie main non-$

#deb http://mirrordirector.raspbian.org/raspbian/ jessie main contrib non-free $

# Uncomment line below then 'apt-get update' to enable 'apt-get source'

#deb-src http://archive.raspbian.org/raspbian/ jessie main contrib non-free rpi