最近更新cocoapods一直失败，提示[!] Failed to connect to GitHub to update the CocoaPods/Specs specs repo - Please check if you are offline, or that GitHub is down
一开始以为是是网络问题，翻墙，热点，切换网络都失败，google一番，Stack Overflow 提示需要更新openssl
$ which openssl
/usr/bin/openssl
$ openssl version
OpenSSL 0.9.8zh 14 Jan 2016
/usr/bin/ruby -e "$(curl -fsSL https://raw.githubusercontent.com/Homebrew/install/master/install)"
$ brew update
$ brew install openssl
$ brew upgrade openssl
`` If you need to have this software first in your PATH run: echo 'export PATH="/usr/local/opt/openssl/bin:$PATH"' >> ~/.bash_profile
$ echo 'export PATH="/usr/local/opt/openssl/bin:$PATH"' >> ~/.bash_profile
$ source ~/.bash_profile
$ which openssl
/usr/local/opt/openssl/bin/openssl
$ openssl version
OpenSSL 1.0.2n 7 Dec 2017
$ brew install rbenv ruby-build
$ echo 'export PATH="$HOME/.rbenv/bin:$PATH"' >> ~/.bash_profile
$ echo 'if which rbenv > /dev/null; then eval "$(rbenv init -)"; fi' >> ~/.bash_profile
$ source ~/.bash_profile
$ rbenv install --list
Available versions:
1.8.5-p52
1.8.5-p113
1.8.5-p114
1.8.5-p115
1.8.5-p231
1.8.6
:
2.1.0
2.1.1
2.1.2
:
$ rbenv install 2.1.0
$ rbenv versions
* system (set by /Users/username/.rbenv/version)
2.1.0
$ ruby --version
ruby 2.0.0p648 (2015-12-16 revision 53162) [universal.x86_64-darwin16]
$ rbenv global 2.1.0
$ rbenv versions
system
* 2.1.0 (set by /Users/username/.rbenv/version)
$ ruby --version
ruby 2.1.0p0 (2013-12-25 revision 44422) [x86_64-darwin16.0]
$ gem install cocoapods -n /usr/local/bin
$ which pod
/usr/local/bin/pod
$ pod --version
1.4.0
正常来说，按照上面的步骤更新成功就可以了，但是，终端提示
curl: (7) Failed to connect to raw.githubusercontent.com port 443: Connection refused
最后发现原因是raw.githubusercontent.com被墙。
解决方法是更改host之后再更新
解决步骤如下
1、查询真实的ip地址
raw.githubusercontent.com 查询真实的IP地址，现在查到的是 151.101.40.133。
2、终端输入命令，并输入密码
sudo vi /etc/hosts
3、将以下文本放于文字最后
151.101.40.133 raw.githubusercontent.com
4、成功，重新pod install 即可
