Drop rails version 4.2, 5.0 and 5.1

According to Rails Guide, it seems that v4.2 and 5.0 and 5.1 have also already
been unsupported versions. So I'm going to drop them in CI config.

See at: https://guides.rubyonrails.org/maintenance_policy.html#security-issues

Author: yhirano55

.travis.yml

@@ -8,9 +8,6 @@ rvm:
   - ruby-head
   - jruby-head
 gemfile:
-  - gemfiles/rails42.gemfile
-  - gemfiles/rails50.gemfile
-  - gemfiles/rails51.gemfile
   - gemfiles/rails52.gemfile
   - gemfiles/rails60.gemfile
   - gemfiles/rails_edge.gemfile

Appraisals

@@ -1,21 +1,3 @@
-appraise "rails42" do
-  gem "rails", "~> 4.2.0"
-  gem "sprockets", "< 4.0"
-  gem "sass-rails", "~> 5.0"
-end
-
-appraise "rails50" do
-  gem "rails", "~> 5.0.0"
-  gem "sprockets", "< 4.0"
-  gem "sass-rails", "~> 5.0"
-end
-
-appraise "rails51" do
-  gem "rails", "~> 5.1.0"
-  gem "sprockets", "< 4.0"
-  gem "sass-rails", "~> 5.0"
-end
-
 appraise "rails52" do
   gem "rails", "~> 5.2.0"
   gem "sprockets", "< 4.0"

README.md

@@ -14,7 +14,7 @@ Framework](http://compass-style.org) for [Ruby on Rails](http://rubyonrails.org/
 
 Since Compass v0.12.0, this is the only way to use compass with your rails application.
 
-Supports Rails 4.2, 5.x and 6.x releases.
+Supports Rails 5.2 and 6.x releases.
 
 ## Installation
 

gemfiles/rails42.gemfile

@@ -7,28 +7,19 @@ module RailsHelpers
         RAILS_6_1   = "6.1"
         RAILS_6_0   = "6.0"
         RAILS_5_2   = "5.2"
-        RAILS_5_1   = "5.1"
-        RAILS_5_0   = "5.0"
-        RAILS_4_2   = "4.2"
 
         WORKING_DIR = File.join(ROOT_PATH, 'rails-temp')
 
         VERSION_LOOKUP = {
           RAILS_6_1 => %r{^6\.1\.},
           RAILS_6_0 => %r{^6\.0\.},
           RAILS_5_2 => %r{^5\.2\.},
-          RAILS_5_1 => %r{^5\.1\.},
-          RAILS_5_0 => %r{^5\.0\.},
-          RAILS_4_2 => %r{^4\.2\.},
         }
 
         GEMFILES = {
           RAILS_6_1 => GEMFILES_DIR.join("rails_edge.gemfile").to_s,
           RAILS_6_0 => GEMFILES_DIR.join("rails60.gemfile").to_s,
           RAILS_5_2 => GEMFILES_DIR.join("rails52.gemfile").to_s,
-          RAILS_5_1 => GEMFILES_DIR.join("rails51.gemfile").to_s,
-          RAILS_5_0 => GEMFILES_DIR.join("rails50.gemfile").to_s,
-          RAILS_4_2 => GEMFILES_DIR.join("rails42.gemfile").to_s,
         }
 
         GENERATOR_OPTIONS = ['-q', '-G', '-O', '--skip-bundle']