fix: Gemfile & Gemfile.lock to reduce vulnerabilities

The following vulnerabilities are fixed with an upgrade:
- https://snyk.io/vuln/SNYK-RUBY-ACTIONPACK-569599
- https://snyk.io/vuln/SNYK-RUBY-ACTIONPACK-569600
- https://snyk.io/vuln/SNYK-RUBY-ACTIVESUPPORT-569598

Gemfile

@@ -1,34 +1,34 @@
 source :rubygems
 
-gem 'rails', '3.1.0'
+gem 'rails', '5.2.4.3'
 
 # Bundle edge Rails instead:
 # gem 'rails',     :git => 'git://github.com/rails/rails.git'
 
 gem 'mysql2'
 
-  gem 'sass-rails', "  ~> 3.1.0"
+  gem 'sass-rails', '~> 5.0.5'
 # Gems used only for assets and not required
 # in production environments by default.
 group :assets do
 
-  gem 'coffee-rails', "~> 3.1.0"
+  gem 'coffee-rails', '~> 4.2.2'
   gem 'uglifier'
 end
 
-gem 'jquery-rails'
+gem 'jquery-rails', '>= 4.0.1'
 
 gem 'high_voltage',     '~> 0.9'
 
-gem 'kaminari',         '~> 0.12.4'
+gem 'kaminari', '~> 0.12.4'
 gem "compass", "~> 0.11.5"
-gem 'simple_form',      '~> 1.4.0'
+gem 'simple_form', '~> 4.0.0'
 gem 'friendly_id',      '~> 3.2.1'
 
 # RSpec needs to be in :development group to expose generators
 # and rake tasks without having to type RAILS_ENV=test.
 group :development, :test do
-  gem 'rspec-rails',  '~> 2.6.0'
+  gem 'rspec-rails', '~> 2.8.0'
 end
 
 group :production, :staging do