fix: Gemfile to reduce vulnerabilities

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

Author: snyk-bot

Gemfile

@@ -4,7 +4,7 @@ source "https://rubygems.org"
 
 git_source(:github) {|repo_name| "https://github.com/#{repo_name}" }
 
-gem "sinatra", "2.0.1"
+gem "sinatra", "4.1.0"
 gem "puma", "4.2.1" 
 gem 'puma-metrics'