Update guard requirement from ~> 2.18.0 to ~> 2.19.0

Updates the requirements on [guard](https://github.com/guard/guard) to permit the latest version.
- [Release notes](https://github.com/guard/guard/releases)
- [Commits](guard/guard@v2.18.0...v2.19.0)

---
updated-dependencies:
- dependency-name: guard
  dependency-type: direct:development
...

Signed-off-by: dependabot[bot] <[email protected]>

Gemfile

@@ -4,7 +4,7 @@ source 'https://rubygems.org'
 gemspec
 
 group :test do
-  gem "guard", "~> 2.18.0"
+  gem "guard", "~> 2.19.0"
   gem "guard-minitest", "~> 2.4.6"
   gem "pry-byebug", "~> 3.10.1"
   gem "pry-doc", "~> 1.4.0"