Drop support to Ruby < 2.4, update travis to run on latest versions

.travis.yml

@@ -1,12 +1,10 @@
 cache: bundler
 language: ruby
 rvm:
-  - 2.3.8
-  - 2.4.6
-  - 2.5.5
-  - 2.6.5
-  - 2.7.0
-  - jruby-9.2.7.0
+  - 2.4
+  - 2.5
+  - 2.6
+  - 2.7
 gemfile:
   - gemfiles/Gemfile.rails-5-0-stable
   - gemfiles/Gemfile.rails-5-1-stable
@@ -14,17 +12,14 @@ gemfile:
   - Gemfile
 matrix:
   exclude:
-    - rvm: 2.3.8
-      gemfile: Gemfile
-    - rvm: 2.4.6
-      gemfile: Gemfile
-    - rvm: jruby-9.1.17.0
-      gemfile: Gemfile
-  allow_failures:
-    - rvm: jruby-9.1.17.0
-      gemfile: Gemfile
-    - rvm: jruby-9.2.7.0
+    - rvm: 2.4
       gemfile: Gemfile
+    - rvm: 2.7
+      gemfile: gemfiles/Gemfile.rails-5-0-stable
+    - rvm: 2.7
+      gemfile: gemfiles/Gemfile.rails-5-1-stable
+    - rvm: 2.7
+      gemfile: gemfiles/Gemfile.rails-5-2-stable
 before_install:
   - gem update --system
 notifications:

CHANGELOG.md

@@ -1,3 +1,7 @@
+## Unreleased
+
+* Drop support to Ruby < 2.4.
+
 ## 5.0.3
 
 ### Bug fix

simple_form.gemspec

@@ -18,7 +18,7 @@ Gem::Specification.new do |s|
   s.test_files   -= Dir["test/support/country_select/**/*"]
   s.require_paths = ["lib"]
 
-  s.required_ruby_version = '>= 2.3.0'
+  s.required_ruby_version = '>= 2.4.0'
 
   s.add_dependency('activemodel', '>= 5.0')
   s.add_dependency('actionpack', '>= 5.0')