fix: Gemfile to reduce vulnerabilities (#34)

The following vulnerabilities are fixed with an upgrade:
- https://snyk.io/vuln/SNYK-RUBY-SINATRA-6483832

Co-authored-by: snyk-bot <[email protected]>

Author: jufemaiz

Gemfile

@@ -9,7 +9,7 @@ source 'https://rubygems.org' do
   gem 'puma'
   gem 'rack', '>= 3.0.0'
   gem 'sass'
-  gem 'sinatra', '>= 2.2.3'
+  gem 'sinatra', '>= 4.1.0'
 
   group :development do
     gem 'rubocop'