bump required ruby and puppet versions

puppet-strings.gemspec

@@ -7,7 +7,7 @@ Gem::Specification.new do |s|
   s.email = 'info@puppet.com'
   s.homepage = 'https://github.com/puppetlabs/puppet-strings'
   s.description = s.summary
-  s.required_ruby_version = '>= 1.9.3'
+  s.required_ruby_version = '>= 2.1.9'
 
   s.extra_rdoc_files = [
     'CHANGELOG.md',
@@ -20,5 +20,5 @@ Gem::Specification.new do |s|
 
   s.add_runtime_dependency 'yard', '~> 0.9.5'
   s.add_runtime_dependency 'rgen'
-  s.requirements << 'puppet, >= 3.7.0'
+  s.requirements << 'puppet, >= 4.0.0'
 end