[elasticsearch] Set version to 2.3.1
[elasticsearch] Set version to 2.3.1

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