RACC 1.6 was released without an accompanying java artifact for jruby. This patch pins racc in logstash-core.

pin-racc-pending-release-of-1.6-artifact-for-java.patch

diff --git a/logstash-core/logstash-core.gemspec b/logstash-core/logstash-core.gemspec
index e22a9f289..a4563498a 100644
--- a/logstash-core/logstash-core.gemspec
+++ b/logstash-core/logstash-core.gemspec
@@ -78,4 +78,8 @@ Gem::Specification.new do |gem|
   gem.add_dependency 'down', '~> 5.2.0' #(MIT license)
   gem.add_dependency 'tzinfo-data' #(MIT license)
   gem.add_dependency 'rufus-scheduler' #(MIT license)
+
+  # TEMPORARY: racc-1.6.0 doesn't have JAVA counterpart (yet)
+  # SEE: https://github.com/ruby/racc/issues/172
+  gem.add_runtime_dependency "racc", "~> 1.5.2" #(Ruby license)
 end