[core] Upgrade to HdrHistogram 2.1.4
[core] Upgrade to HdrHistogram 2.1.4

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