Capistrano 报错 `raiseUnlessLoaded': OpenSSH keys only supported if ED25519 is available (NotImplem...

Capistrano 部署时报如下错误

# terminated with exception (report_on_exception is true):
/Library/Ruby/Gems/2.6.0/gems/net-ssh-6.1.0/lib/net/ssh/authentication/ed25519_loader.rb:21:in `raiseUnlessLoaded': OpenSSH keys only supported if ED25519 is available (NotImplementedError)
net-ssh requires the following gems for ed25519 support:
 * ed25519 (>= 1.2, < 2.0)
 * bcrypt_pbkdf (>= 1.0, < 2.0)
See https://github.com/net-ssh/net-ssh/issues/565 for more information
Gem::MissingSpecError : "Could not find 'ed25519' (~> 1.2) among 55 total gem(s)
Checked in 'GEM_PATH=/Users/machao/.gem/ruby/2.6.0:/Library/Ruby/Gems/2.6.0:/System/Library/Frameworks/Ruby.framework/Versions/2.6/usr/lib/ruby/gems/2.6.0', execute `gem env` for more information"

解决办法

# 在执行 cap 的机器执行下面命令
ssh-add