Use --format and --out flags

puppet-strings removed the deprecated `emit_*` flags, so use the modern replacements.

See puppetlabs/puppet-strings#329

Author: joshcooper

lib/puppet_references/puppet/strings.rb

@@ -23,7 +23,7 @@ def initialize(force_cached = false)
       def generate_strings_data
         puts 'Generating Puppet Strings JSON data...'
         rubyfiles = Dir.glob("#{PuppetReferences::PUPPET_DIR}/lib/puppet/**/*.rb")
-        system("bundle exec puppet strings generate --emit-json #{STRINGS_JSON_FILE} #{rubyfiles.join(' ')}")
+        system("bundle exec puppet strings generate --format json --out #{STRINGS_JSON_FILE} #{rubyfiles.join(' ')}")
         puts "Strings data: Done! (#{STRINGS_JSON_FILE})"
         @@strings_data_cached = true
       end