Add dependency on base64 (for ruby 3.4)

Author: nevans

vault.gemspec

@@ -22,6 +22,7 @@ Gem::Specification.new do |spec|
 
   spec.required_ruby_version = ">= 3.1"
   spec.add_runtime_dependency "aws-sigv4"
+  spec.add_runtime_dependency "base64"
 
   spec.add_development_dependency "bundler", "~> 2"
   spec.add_development_dependency "pry",     "~> 0.13.1"