iOS安装cocoapods时会遇到各种各样的问题，比如最近出现的一个问题，在pod setup之后会出现
Failed to connect to GitHub to update the CocoaPods/Specs specs repo – Please check if you are offline, or that GitHub is down 错误
解决办法：

$ 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
:
  2.5.0-rc1
  2.5.0
  2.6.0-dev
:

$ rbenv install 2.5.0

$ rbenv versions
* system (set by /Users/username/.rbenv/version)
  2.5.0

$ ruby --version
ruby 2.0.0p648 (2015-12-16 revision 53162) [universal.x86_64-darwin16]

$ rbenv global 2.5.0

$ rbenv versions
  system
* 2.5.0 (set by /Users/username/.rbenv/version)

$ ruby --version
ruby 2.5.0p0 (2017-12-25 revision 61468) [x86_64-darwin16]

$ gem install cocoapods -n /usr/local/bin

$ which pod
/usr/local/bin/pod

$ pod --version
1.4.0

完成上面一系列操作后，Cocoapods将会升级到最新的1.4.0版本。
然后就可以继续pod setup了。