參考：https://www.cnblogs.com/xuhaoforwards/p/9399744.html
安裝ROS過程中運行sudo rosdep init后，出現如下錯誤LOG：
ERROR: cannot download default sources list from: https://raw.githubusercontent.com/ros/rosdistro/master/rosdep/sources.list.d/20-default.list Website may be down.
解決辦法
sudo apt-get install python-wstool