Drop Rails 5.1 support

Author: deivid-rodriguez

.travis.yml

@@ -6,7 +6,6 @@ rvm:
   - 2.6.3
   - ruby-head
 env:
-  - RAILS_VERSION="~> 5.1.0"
   - RAILS_VERSION="~> 5.2.0"
   - RAILS_VERSION="~> 6.0.0.rc1"
 matrix:

README.md

@@ -17,7 +17,7 @@ boot it every time you run a test, rake task or migration.
 ## Compatibility
 
 * Ruby versions: MRI 2.4, MRI 2.5, MRI 2.6
-* Rails versions: 5.1, 5.2, 6.0 (Spring is installed by default when you do
+* Rails versions: 5.2, 6.0 (Spring is installed by default when you do
   `rails new` to generate your application)
 
 Spring makes extensive use of `Process.fork`, so won't be able to

lib/spring/application.rb

@@ -91,8 +91,8 @@ def preload
 
       require Spring.application_root_path.join("config", "application")
 
-      unless Rails.respond_to?(:gem_version) && Rails.gem_version >= Gem::Version.new('5.1.0')
-        raise "Spring only supports Rails >= 5.1.0"
+      unless Rails.respond_to?(:gem_version) && Rails.gem_version >= Gem::Version.new('5.2.0')
+        raise "Spring only supports Rails >= 5.2.0"
       end
 
       # config/environments/test.rb will have config.cache_classes = true. However
@@ -163,13 +163,7 @@ def serve(client)
       setup command
 
       if Rails.application.reloaders.any?(&:updated?)
-        # Rails 5.1 forward-compat. AD::R is deprecated to AS::R in Rails 5.
-        if defined? ActiveSupport::Reloader
-          Rails.application.reloader.reload!
-        else
-          ActionDispatch::Reloader.cleanup!
-          ActionDispatch::Reloader.prepare!
-        end
+        Rails.application.reloader.reload!
       end
 
       pid = fork {