Update vault-ruby dependency to ~> 0.20

Updated the vault gem dependency from ~> 0.19 to ~> 0.20 to use the
newly released vault-ruby 0.20.0.

Author: chrisarcand

CHANGELOG.md

@@ -9,6 +9,7 @@ BREAKING CHANGES
 
 IMPROVEMENTS
 
+- Updated vault-ruby dependency from ~> 0.19 to ~> 0.20
 - Restored Rails version matrix testing in CI (was accidentally dropped during CircleCI to GitHub Actions migration)
 - Updated CI to test currently supported Rails versions: 7.2, 8.0, 8.1
 - Updated CI to test Ruby versions: 3.2, 3.3, 3.4, 4.0

vault.gemspec

@@ -20,7 +20,7 @@ Gem::Specification.new do |s|
   s.required_ruby_version = ">= 3.2"
 
   s.add_dependency "activesupport", ">= 7.0"
-  s.add_dependency "vault", "~> 0.19"
+  s.add_dependency "vault", "~> 0.20"
   # mutex_m was removed from Ruby's default gems in 3.4.0
   s.add_dependency "mutex_m"
   # bigdecimal was removed from Ruby's default gems in 3.4.0