(PA-5341) Update minimum Ruby version to 2.7

This commit updates the minimum version of Ruby to run semantic_puppet
from 1.9.3 to 2.7.0 in the gemspec, and updates the README to reflect
that change.

Author: mhashizume

README.md

@@ -19,8 +19,7 @@ This library is used by a number of Puppet Labs projects, including
 Requirements
 ------------
 
-Semantic_puppet will work on several ruby versions, including 1.9.3,
-2.0.0, 2.1.9 and 2.4.1. Please see the exact matrix in `.travis.yml`.
+semantic_puppet will work on Ruby version 2.7 and greater.
 
 No gem/library requirements.
 

semantic_puppet.gemspec

@@ -20,7 +20,7 @@ spec = Gem::Specification.new do |s|
   s.require_paths = ["lib"]
 
   # Dependencies
-  s.required_ruby_version = '>= 1.9.3'
+  s.required_ruby_version = '>= 2.7.0'
 
   s.add_development_dependency "json", "~> 1.8.3" if RUBY_VERSION < '2.0'
   s.add_development_dependency "rake"