Update minimum Ruby constriant to 2.5

.github/workflows/testing.yml

@@ -22,7 +22,7 @@ jobs:
     runs-on: ubuntu-18.04
     strategy:
       matrix:
-        ruby: [ '2.4.x', '2.5.x', '2.6.x' ]
+        ruby: [ '2.5.x', '2.6.x', '2.7.x' ]
     name: Vagrant unit tests on Ruby ${{ matrix.ruby }}
     steps:
       - name: Code Checkout

vagrant.gemspec

@@ -12,7 +12,7 @@ Gem::Specification.new do |s|
   s.summary       = "Build and distribute virtualized development environments."
   s.description   = "Vagrant is a tool for building and distributing virtualized development environments."
 
-  s.required_ruby_version     = "~> 2.4", "< 2.8"
+  s.required_ruby_version     = "~> 2.5", "< 2.8"
   s.required_rubygems_version = ">= 1.3.6"
 
   s.add_dependency "bcrypt_pbkdf", "~> 1.0.0"