Bump ruby to 2.6.6 and speed up docker build

Gemfile

@@ -1,24 +1,22 @@
 source 'https://rubygems.org'
 git_source(:github) { |repo| "https://github.com/#{repo}.git" }
 
-ruby '2.6.3'
+ruby '2.6.6'
 
-# Bundle edge Rails instead: gem 'rails', github: 'rails/rails'
 gem 'rails', '6.0.4.7'
-# Use postgresql as the database for Active Record
+
 gem 'pg', '>= 0.18', '< 2.0'
-# Use Puma as the app server
+
 gem 'puma', '~> 4.3'
-# Use SCSS for stylesheets
 gem 'sass-rails', '~> 5'
-# Transpile app-like JavaScript. Read more: https://github.com/rails/webpacker
+gem 'sassc', '2.1.0' # temporarely, because 2.4.0 takes 5 minutes to install...
+
 gem 'webpacker', '~> 4.0'
-# Turbolinks makes navigating your web application faster. Read more: https://github.com/turbolinks/turbolinks
+
 gem 'turbolinks', '~> 5'
-# Build JSON APIs with ease. Read more: https://github.com/rails/jbuilder
+
 gem 'jbuilder', '~> 2.7'
 
-# Reduces boot times through caching; required in config/boot.rb
 gem 'bootsnap', '>= 1.4.2', require: false
 
 # Authentication
@@ -34,7 +32,6 @@ gem 'react-rails', '~> 2.6.0'
 gem 'kaminari', '~> 1.2.1'
 
 group :development, :test do
-  # Call 'byebug' anywhere in the code to stop execution and get a debugger console
   gem 'byebug', platforms: [:mri, :mingw, :x64_mingw]
 
   gem 'rspec-rails', '~> 3.8.2'
@@ -42,10 +39,8 @@ group :development, :test do
 end
 
 group :development do
-  # Access an interactive console on exception pages or by calling 'console' anywhere in the code.
   gem 'web-console', '>= 3.3.0'
   gem 'listen', '>= 3.0.5', '< 3.2'
-  # Spring speeds up development by keeping your application running in the background. Read more: https://github.com/rails/spring
   gem 'spring'
   gem 'spring-watcher-listen', '~> 2.0.0'
 end