rubyバージョンの低さによるCocoapodsエラー

以前正常に使用していたCocoapods、pod updateの時に突然エラーが発生しました:

/Library/Ruby/Site/2.0.0/rubygems/dependency.rb:308:in `to_specs': Could not find 'cocoapods' (>= 0) among 33 total gem(s) (Gem::MissingSpecError)

Checked in 'GEM_PATH=/Users/JinXiaoHao/.rvm/gems/ruby-2.0.0-p648:/Users/JinXiaoHao/.rvm/gems/ruby-2.0.0-p648@global',execute `gem env` for more information

from/Library/Ruby/Site/2.0.0/rubygems/dependency.rb:320:in `to_spec'

from/Library/Ruby/Site/2.0.0/rubygems/core_ext/kernel_gem.rb:65:in `gem'

from /usr/local/bin/pod:22:in `'

ここではまず端末でルビーのバージョンを見ることができます
$ruby -v ruby 2.0.0p648 (2015-12-16 revision 53162) [x86_64-darwin15.4.0]
$gem sources--remove https://rubygems.org/source https://rubygems.org/ not present in cache
$gem sources -a https://ruby.taobao.org/source https://ruby.taobao.org/ already present in the cache
$gem sources -l *** CURRENT SOURCES *** https://ruby.taobao.org/
$ sudo gem installcocoapods ERROR: Error installing cocoapods: activesupport requires Ruby version >= 2.2.2.
以上は問題を解決していません.以下はポイントです.
ルビーを更新して、終わったらpodsをインストールすればいいです
$rvm install 2.2.4
$sudo gem installcocoapods