1.需要安装ruby最新版时安装不上
使用cocopod时，需To install do: 'rvm install "ruby-2.6.0"'；运行rvm install "ruby-2.6.0时，遇到：
Error running './configure --prefix=/Users/mc/.rvm/rubies/ruby-2.6.0 --with-opt-dir=/usr/local/opt/libyaml:/usr/local/opt/readline:/usr/local/opt/libksba:/usr/local/opt/openssl@1.1 --disable-install-doc --enable-shared',
please read /Users/mc/.rvm/log/1571023136_ruby-2.6.0/configure.log
There has been an error while running configure. Halting the installation.
解决办法：
1.先运行：xcode-select --install
2.再运行：rvm install "ruby-2.6.0“
2.运行pod install，出现以下问题：
Traceback(most recent call last):
2: from /usr/local/bin/pod:23:in ‘<main>’
1: from /Users/mc/.rvm/rubies/ruby-2.5.1/lib/ruby/site_ruby/2.5.0/rubygems.rb:308:in `activate_bin_path'
/Users/mc/.rvm/rubies/ruby-2.5.1/lib/ruby/site_ruby/2.5.0/rubygems.rb:289:in `find_spec_for_exe':can't find gem cocoapods (>= 0.a) with executable pod (Gem::GemNotFoundException)
解决方法：
1、sudo gem update --system
2、gem install cocoapods
