Improve Docker installation (#152)

Gemfile

@@ -2,22 +2,21 @@ source 'https://rubygems.org'
 git_source(:github) { |repo| "https://github.com/#{repo}.git" }
 
 ruby '2.6.6'
+gem 'rake', '12.3.3'
 
 gem 'rails', '6.0.5'
 
-gem 'pg', '>= 0.18', '< 2.0'
+gem 'pg', '1.3.5'
 
-gem 'puma', '~> 4.3'
-
-gem 'sass-rails', '~> 5'
+gem 'puma', '4.3.12'
 
 gem 'webpacker', '4.3.0'
 
-gem 'turbolinks', '~> 5'
+gem 'turbolinks', '5.2.1'
 
-gem 'jbuilder', '~> 2.7'
+gem 'jbuilder', '2.11.5'
 
-gem 'bootsnap', '>= 1.4.2', require: false
+gem 'bootsnap', '1.12.0', require: false
 
 # HTTP requests
 gem 'httparty', '0.18.0'
@@ -29,13 +28,13 @@ gem 'devise', '4.7.3'
 gem 'pundit', '2.2.0'
 
 # I18n (forward locales to JS)
-gem 'i18n-js'
+gem 'i18n-js', '3.9.2'
 
 # React
-gem 'react-rails', '~> 2.6.0'
+gem 'react-rails', '2.6.2'
 
 # Pagination
-gem 'kaminari', '~> 1.2.1'
+gem 'kaminari', '1.2.2'
 
 group :development, :test do
   gem 'byebug', platforms: [:mri, :mingw, :x64_mingw]
@@ -46,7 +45,6 @@ end
 
 group :development do
   gem 'web-console', '>= 3.3.0'
-  gem 'listen', '>= 3.0.5', '< 3.2'
   gem 'spring'
   gem 'spring-watcher-listen', '~> 2.0.0'
 end
@@ -59,5 +57,8 @@ group :test do
   gem 'webdrivers'
 end
 
+# If not bundled, webpack compilation in production fails
+gem 'listen', '>= 3.0.5', '< 3.2'
+
 # Windows does not include zoneinfo files, so bundle the tzinfo-data gem
 gem 'tzinfo-data', platforms: [:mingw, :mswin, :x64_mingw, :jruby]