部署老系统出现的问题Gem::InstallError: net-ssh requires Ruby version >= 2.0

gem ‘unicorn‘

group :test, :development do
  gem "rspec-rails", ">= 2.5.0"
  gem ‘factory_girl‘, ‘2.6.4‘
  gem ‘factory_girl_rails‘, ‘1.7.0‘
  gem ‘faker‘, ‘1.1.2‘
  gem ‘forgery‘, ‘0.5.0‘
  gem ‘magic_encoding‘, ‘0.0.2‘
  gem ‘email_spec‘, ‘1.4.0‘

  gem ‘net-ssh‘, ‘~> 2.0‘
  gem ‘capistrano‘, ‘~> 2.15.7‘
  gem ‘capistrano-rbenv‘, ‘1.0.5‘
  gem ‘rb-readline‘,‘0.4.2‘
end