fix: Gemfile to reduce vulnerabilities

The following vulnerabilities are fixed with an upgrade:
- https://snyk.io/vuln/SNYK-RUBY-ACTIONCABLE-20338

Gemfile

@@ -6,7 +6,7 @@ git_source(:github) { |repo| "https://github.com/#{repo}.git" }
 ruby '~> 2.6'
 
 # Bundle edge Rails instead: gem 'rails', github: 'rails/rails'
-gem 'rails', '~> 6.1.4'
+gem 'rails', '~> 7.1.0'
 # Use sqlite3 as the database for Active Record
 gem 'sqlite3', '~> 1.4'
 # Use Puma as the app server