[elasticearch] upgrade to version 2.3.4
[elasticearch] upgrade to version 2.3.4

This commit upgrades the Elasticsearch dependency from version 2.3.2 to
version 2.3.4

madhurihn/YCSB_ToyDB,cricket007/YCSB,ChristianNavolskyi/YCSB,zyguan/ycsb,brianfrankcooper/YCSB,madhurihn/YCSB_ToyDB,cricket007/YCSB,cricket007/YCSB,ChristianNavolskyi/YCSB,jaemyoun/YCSB,manolama/YCSB,manolama/YCSB,zyguan/ycsb,zyguan/ycsb,ChristianNavolskyi/YCSB,madhurihn/YCSB_ToyDB,jaemyoun/YCSB,brianfrankcooper/YCSB,leschekhomann/YCSB,jaemyoun/YCSB,leschekhomann/YCSB,ChristianNavolskyi/YCSB,manolama/YCSB,zyguan/ycsb,jaemyoun/YCSB,cricket007/YCSB,brianfrankcooper/YCSB,manolama/YCSB,madhurihn/YCSB_ToyDB,leschekhomann/YCSB,brianfrankcooper/YCSB,leschekhomann/YCSB