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]

split-analytics.gemspec

@@ -19,6 +19,6 @@ Gem::Specification.new do |gem|
   gem.add_dependency('split', '>= 3.0.0')
 
   gem.add_development_dependency('rspec', '~> 3.1')
-  gem.add_development_dependency('rake', '~> 12.3')
+  gem.add_development_dependency('rake', '~> 13.0')
   gem.add_development_dependency('fakeredis', '~> 0.7')
 end