Update rake requirement from ~> 12.3 to ~> 13.0

Updates the requirements on [rake](https://github.com/ruby/rake) to permit the latest version.
- [Release notes](https://github.com/ruby/rake/releases)
- [Changelog](https://github.com/ruby/rake/blob/master/History.rdoc)
- [Commits](ruby/rake@v12.3.0...v13.0.0)

Signed-off-by: dependabot-preview[bot] <support@dependabot.com>

Author: dependabot-preview[bot]

sensu-plugins-filesystem-checks.gemspec

@@ -40,7 +40,7 @@ Gem::Specification.new do |s|
   s.add_development_dependency 'codeclimate-test-reporter', '~> 0.4'
   s.add_development_dependency 'github-markup',             '~> 3.0'
   s.add_development_dependency 'pry',                       '~> 0.10'
-  s.add_development_dependency 'rake',                      '~> 12.3'
+  s.add_development_dependency 'rake',                      '~> 13.0'
   s.add_development_dependency 'redcarpet',                 '~> 3.2'
   s.add_development_dependency 'rspec',                     '~> 3.1'
   s.add_development_dependency 'rubocop',                   '~> 0.40.0'