Add a missing base64 require.

Also, prepare for the moving of base64 from default to a bundled gem in ruby 3.4.

Gemfile.lock

@@ -3,6 +3,7 @@ PATH
   specs:
     kamal (1.3.0)
       activesupport (>= 7.0)
+      base64 (~> 0.2)
       bcrypt_pbkdf (~> 1.0)
       concurrent-ruby (~> 1.2)
       dotenv (~> 2.8)

kamal.gemspec

@@ -20,6 +20,7 @@ Gem::Specification.new do |spec|
   spec.add_dependency "ed25519", "~> 1.2"
   spec.add_dependency "bcrypt_pbkdf", "~> 1.0"
   spec.add_dependency "concurrent-ruby", "~> 1.2"
+  spec.add_dependency "base64", "~> 0.2"
 
   spec.add_development_dependency "debug"
   spec.add_development_dependency "mocha"

lib/kamal/commands/lock.rb

@@ -1,5 +1,6 @@
 require "active_support/duration"
 require "time"
+require "base64"
 
 class Kamal::Commands::Lock < Kamal::Commands::Base
   def acquire(message, version)