Rubocop, in preparation for pre-release rake task that sanity checks for release

Rakefile

@@ -1,9 +1,9 @@
-require "logstash/devutils/rake"
+require 'logstash/devutils/rake'
 require 'jars/installer'
 
-desc "Fetch any jars required for this plugin"
+desc 'Fetch any jars required for this plugin'
 task :install_jars do
-  ENV['JARS_HOME'] = Dir.pwd + "/vendor/jar-dependencies/runtime-jars"
-  ENV['JARS_VENDOR'] = "false"
+  ENV['JARS_HOME'] = Dir.pwd + '/vendor/jar-dependencies/runtime-jars'
+  ENV['JARS_VENDOR'] = 'false'
   Jars::Installer.new.vendor_jars!(false)
 end