Update Gemfile.lock
Update Gemfile.lock

Summary:
bump nokogiri number
Closes https://github.com/facebook/rocksdb/pull/3358

Differential Revision: D6708596

Pulled By: ajkr

fbshipit-source-id: 6662c3ba4994374ecf8a13928e915b655a980b70

SunguckLee/RocksDB,SunguckLee/RocksDB,SunguckLee/RocksDB,SunguckLee/RocksDB,SunguckLee/RocksDB,SunguckLee/RocksDB,SunguckLee/RocksDB,SunguckLee/RocksDB