Drop support for ruby 2.4

Since it reached its End of Life too.

Author: deivid-rodriguez

Diff for: .travis.yml

@@ -1,17 +1,13 @@
 language: ruby
 cache: bundler
 rvm:
-  - 2.4.6
   - 2.5.5
   - 2.6.3
   - ruby-head
 env:
   - RAILS_VERSION="~> 5.2.0"
   - RAILS_VERSION="~> 6.0.0.rc1"
 matrix:
-  exclude:
-    - rvm: 2.4.6
-      env: RAILS_VERSION="~> 6.0.0.rc1"
   allow_failures:
     - rvm: ruby-head
   fast_finish: true

Diff for: README.md

@@ -16,7 +16,7 @@ boot it every time you run a test, rake task or migration.
 
 ## Compatibility
 
-* Ruby versions: MRI 2.4, MRI 2.5, MRI 2.6
+* Ruby versions: MRI 2.5, MRI 2.6
 * Rails versions: 5.2, 6.0 (Spring is installed by default when you do
   `rails new` to generate your application)
 

Diff for: spring.gemspec

@@ -13,7 +13,7 @@ Gem::Specification.new do |gem|
   gem.files         = Dir["LICENSE.txt", "README.md", "lib/**/*", "bin/*"]
   gem.executables   = gem.files.grep(%r{^bin/}).map{ |f| File.basename(f) }
 
-  gem.required_ruby_version = ">= 2.4.0"
+  gem.required_ruby_version = ">= 2.5.0"
 
   gem.add_development_dependency 'rake'
   gem.add_development_dependency 'bump'