Bring back Ruby 2.4 support

Closes: #76

Author: davishmcclurg

.github/workflows/ci.yml

@@ -4,7 +4,7 @@ jobs:
   ruby:
     strategy:
       matrix:
-        ruby: [2.5, 2.6, 2.7, truffleruby-head]
+        ruby: [2.4, 2.5, 2.6, 2.7, truffleruby-head]
     runs-on: ubuntu-latest
     steps:
     - uses: actions/checkout@v2

json_schemer.gemspec

@@ -20,7 +20,7 @@ Gem::Specification.new do |spec|
   spec.executables   = spec.files.grep(%r{^exe/}) { |f| File.basename(f) }
   spec.require_paths = ["lib"]
 
-  spec.required_ruby_version = '~> 2.5'
+  spec.required_ruby_version = '~> 2.4'
 
   spec.add_development_dependency "bundler", "~> 2.0"
   spec.add_development_dependency "rake", "~> 13.0"