极简安装cocoapods

只需要保证ruby和gem有即可，mac自带的有，可以直接安装cocoapods

1、ruby -v
ruby 2.6.3p62 (2019-04-16 revision 67580) [universal.x86_64-darwin19]

2、gem -v
3.0.3

3、sudo gem install -n /usr/local/bin cocoapods
Fetching...
32 gems installed

4、pod --version
1.9.3

5、更新cocoapods
sudo gem install cocoapods

注意：更换gem源
gem sources --remove https://rubygems.org/
gem sources --add https://gems.ruby-china.com