Upgraded to using sintra ~> 4.0 in the specs for Ruby 4.0.

Author: postmodern

Gemfile

@@ -39,7 +39,7 @@ group :development do
 
   gem 'rspec',            '~> 3.0'
   gem 'simplecov',        '~> 0.20'
-  gem 'sinatra',          '~> 3.0'
+  gem 'sinatra',          '~> 4.0'
   gem 'webmock',          '~> 3.0'
 
   gem 'kramdown',         '~> 2.0'