Test failure: Bundler could not find compatible versions for gem "concurrent-ruby"

https://logstash-ci.elastic.co/job/elastic+logstash+master+multijob-acceptance/label=metal,suite=redhat/322/console

```
+ ci/ci_acceptance.sh redhat
Generating the RPM, make sure you start with a clean environment before generating other packages.
Picked up JAVA_TOOL_OPTIONS: -Dfile.encoding=UTF8
Picked up JAVA_TOOL_OPTIONS: -Dfile.encoding=UTF8
Invoking bundler install...
Plugin version conflict, aborting
rake aborted!
Bundler could not find compatible versions for gem "concurrent-ruby":
In snapshot (Gemfile.lock):
concurrent-ruby (= 1.0.0)

In Gemfile:
logstash-core (>= 0) java depends on
concurrent-ruby (>= 1.0.5, ~> 1.0) java
```