[root@app-test ruby-2.2.3]# gem install capistrano -v 2.15

ERROR:  While executing gem ... (Gem::RemoteFetcher::FetchError)

    Errno::ECONNRESET: Connection reset by peer - SSL_connect (https://api.rubygems.org/quick/Marshal.4.8/capistrano-2.15.0.gemspec.rz)

 

后来查找了下原因，在淘宝的网站上发现了相同的描述，才发现是GFW的原因，他们提供了一个gem server。

$ gem sources --remove https://rubygems.org/
$ gem sources -a https://ruby.taobao.org/
$ gem sources -l
*** CURRENT SOURCES ***

https://ruby.taobao.org

更改为taobao的源之后使用gem install即可