Retrieve logstash-core gem's path using inline bundler (#218)

Avoid to fork a bundler process to extract logstash-core's path and use the same bundler that wraps the execution of the Rakefile itself.

Co-authored-by: João Duarte <[email protected]>

Author: andsel

Rakefile

@@ -21,8 +21,8 @@ end
 def delete_create_gradle_properties
   root_dir = File.dirname(__FILE__)
   gradle_properties_file = "#{root_dir}/gradle.properties"
-  lsc_path = `bundle show logstash-core`
-  lsce_path = `bundle show logstash-core-event`
+  # find the path to the logstash-core gem
+  lsc_path = Bundler.rubygems.find_name("logstash-core").first.full_gem_path
   FileUtils.rm_f(gradle_properties_file)
   File.open(gradle_properties_file, "w") do |f|
     f.puts "logstashCoreGemPath=#{lsc_path}"