Update rake requirement from ~> 12.0 to ~> 13.0 (#130)

Merge pull request 130

Author: dependabot[bot]

jemoji.gemspec

@@ -20,7 +20,7 @@ Gem::Specification.new do |s|
   s.add_dependency "jekyll", ">= 3.0", "< 5.0"
 
   s.add_development_dependency "bundler"
-  s.add_development_dependency "rake", "~> 12.0"
+  s.add_development_dependency "rake", "~> 13.0"
   s.add_development_dependency "rspec", "~> 3.0"
   s.add_development_dependency "rubocop-jekyll", "~> 0.4"
 end