Update sinatra requirement from ~> 1.4 to ~> 2.0

Updates the requirements on [sinatra](https://github.com/sinatra/sinatra) to permit the latest version.
- [Release notes](https://github.com/sinatra/sinatra/releases)
- [Changelog](https://github.com/sinatra/sinatra/blob/master/CHANGELOG.md)
- [Commits](sinatra/sinatra@1.4.0...v2.0.7)

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

Author: dependabot-preview[bot]

Gemfile

@@ -3,7 +3,7 @@ gemspec
 
 group :test do
   gem "chefstyle"
-  gem "sinatra", "~> 1.4"
+  gem "sinatra", "~> 2.0"
   gem "rspec",   "~> 3.0"
   gem "webmock", "~> 2.3"
   gem "rainbow", "< 2.2.1"