Move puppet dev dep to Gemfile, add puppet-strings dep (#19)

The 'PUPPET_VERSION' environment variable will be used to install
specific versions of Puppet, and if the version specified supports
puppet-strings, then the dep's added to test the strings parser.

This allows the removal of Gemfile alterations from the Jenkins job and
makes it easier to test different versions in development.

Gemfile

@@ -2,3 +2,11 @@ source 'https://rubygems.org'
 
 # Specify your gem's dependencies in kafo_parsers.gemspec
 gemspec
+
+puppet_version = ENV['PUPPET_VERSION']
+puppet_spec = puppet_version ? "~> #{puppet_version}" : '< 5.0.0'
+gem 'puppet', puppet_spec
+
+if puppet_version.nil? || (puppet_version >= '3.7' && RUBY_VERSION >= '1.9')
+  gem 'puppet-strings'
+end

kafo_parsers.gemspec

@@ -23,7 +23,6 @@ Gem::Specification.new do |spec|
   spec.add_development_dependency "ci_reporter", "~> 1.9.0"
 
   # puppet manifests parsing
-  spec.add_development_dependency 'puppet', '< 5.0.0'
   spec.add_dependency 'rdoc', '>= 3.9.0'
   spec.add_dependency 'json'
 end