关于rosdep update报错

• 问题描述：

rosdep update时常发生如下错误：

$rosdep update

reading in sources list data from /etc/ros/rosdep/sources.list.d
ERROR: unable to process source [https://raw.githubusercontent.com/ros/rosdistro/master/rosdep/osx-homebrew.yaml]:
	 (https://raw.githubusercontent.com/ros/rosdistro/master/rosdep/osx-homebrew.yaml)
ERROR: unable to process source [https://raw.githubusercontent.com/ros/rosdistro/master/rosdep/base.yaml]:
	 (https://raw.githubusercontent.com/ros/rosdistro/master/rosdep/base.yaml)
ERROR: unable to process source [https://raw.githubusercontent.com/ros/rosdistro/master/rosdep/python.yaml]:
	 (https://raw.githubusercontent.com/ros/rosdistro/master/rosdep/python.yaml)
ERROR: unable to process source [https://raw.githubusercontent.com/ros/rosdistro/master/rosdep/ruby.yaml]:
	 (https://raw.githubusercontent.com/ros/rosdistro/master/rosdep/ruby.yaml)
ERROR: unable to process source [https://raw.githubusercontent.com/ros/rosdistro/master/releases/fuerte.yaml]:
	Failed to download target platform data for gbpdistro:
	
Query rosdistro index https://raw.githubusercontent.com/ros/rosdistro/master/index-v4.yaml
ERROR: error loading sources list:
	 (https://raw.githubusercontent.com/ros/rosdistro/master/index-v4.yaml)>

• 解决方法

上述问题是因为DNS污染导致无法访问raw.githubusercontent.com，解决方法是往/etc/hosts文件添加如下内容：

# GitHub 

140.82.113.4    github.com
199.232.28.133    githubusercontent.com
199.232.28.133    raw.githubusercontent.com
192.30.253.112    github.com
192.30.253.113    github.com
192.30.253.119    gist.github.com
192.30.255.112    github.com git 
151.101.185.194    github.global.ssl.fastly.net
151.101.88.249    github.global.ssl.fastly.net
151.101.100.133    assets-cdn.github.com
151.101.100.133    raw.githubusercontent.com
185.31.16.184    github.global.ssl.fastly.net


52.74.223.119 github.com
192.30.253.119 gist.github.com
54.169.195.247 api.github.com
185.199.111.153 assets-cdn.github.com
151.101.76.133 raw.githubusercontent.com
151.101.108.133 user-images.githubusercontent.com
151.101.76.133 gist.githubusercontent.com
151.101.76.133 cloud.githubusercontent.com
151.101.76.133 camo.githubusercontent.com
151.101.76.133 avatars0.githubusercontent.com
151.101.76.133 avatars1.githubusercontent.com
151.101.76.133 avatars2.githubusercontent.com
151.101.76.133 avatars3.githubusercontent.com
151.101.76.133 avatars4.githubusercontent.com
151.101.76.133 avatars5.githubusercontent.com
151.101.76.133 avatars6.githubusercontent.com
151.101.76.133 avatars7.githubusercontent.com
151.101.76.133 avatars8.githubusercontent.com