Update format_version comment
Update format_version comment

Summary: We added a new format version. Reflect that in the comments.

Test Plan: none

Reviewers: sdong, rven, yhchiang, MarkCallaghan

Reviewed By: MarkCallaghan

Subscribers: dhruba, leveldb

Differential Revision: https://reviews.facebook.net/D31629

siddhartharay007/rocksdb,skunkwerks/rocksdb,tsheasha/rocksdb,caijieming-baidu/rocksdb,biddyweb/rocksdb,JackLian/rocksdb,hobinyoon/rocksdb,JackLian/rocksdb,IMCG/RcoksDB,Andymic/rocksdb,Vaisman/rocksdb,biddyweb/rocksdb,vmx/rocksdb,lgscofield/rocksdb,sorphi/rocksdb,JackLian/rocksdb,ylong/rocksdb,flabby/rocksdb,biddyweb/rocksdb,wlqGit/rocksdb,ylong/rocksdb,luckywhu/rocksdb,kaschaeffer/rocksdb,JoeWoo/rocksdb,IMCG/RcoksDB,makelivedotnet/rocksdb,flabby/rocksdb,wat-ze-hex/rocksdb,virtdb/rocksdb,JackLian/rocksdb,facebook/rocksdb,JoeWoo/rocksdb,dkorolev/rocksdb,Applied-Duality/rocksdb,geraldoandradee/rocksdb,geraldoandradee/rocksdb,temicai/rocksdb,dkorolev/rocksdb,anagav/rocksdb,skunkwerks/rocksdb,bbiao/rocksdb,Andymic/rocksdb,lgscofield/rocksdb,kaschaeffer/rocksdb,OverlordQ/rocksdb,temicai/rocksdb,wenduo/rocksdb,Andymic/rocksdb,wat-ze-hex/rocksdb,amyvmiwei/rocksdb,vashstorm/rocksdb,rDSN-Projects/rocksdb.replicated,vmx/rocksdb,jalexanderqed/rocksdb,flabby/rocksdb,JoeWoo/rocksdb,tizzybec/rocksdb,JohnPJenkins/rocksdb,wenduo/rocksdb,anagav/rocksdb,tizzybec/rocksdb,anagav/rocksdb,NickCis/rocksdb,skunkwerks/rocksdb,geraldoandradee/rocksdb,alihalabyah/rocksdb,Applied-Duality/rocksdb,OverlordQ/rocksdb,lgscofield/rocksdb,bbiao/rocksdb,SunguckLee/RocksDB,skunkwerks/rocksdb,vmx/rocksdb,lgscofield/rocksdb,temicai/rocksdb,bbiao/rocksdb,norton/rocksdb,NickCis/rocksdb,mbarbon/rocksdb,facebook/rocksdb,flabby/rocksdb,facebook/rocksdb,tsheasha/rocksdb,amyvmiwei/rocksdb,bbiao/rocksdb,vmx/rocksdb,IMCG/RcoksDB,IMCG/RcoksDB,SunguckLee/RocksDB,Vaisman/rocksdb,jalexanderqed/rocksdb,geraldoandradee/rocksdb,kaschaeffer/rocksdb,luckywhu/rocksdb,wenduo/rocksdb,Vaisman/rocksdb,hobinyoon/rocksdb,luckywhu/rocksdb,wenduo/rocksdb,virtdb/rocksdb,norton/rocksdb,mbarbon/rocksdb,RyanTech/rocksdb,OverlordQ/rocksdb,Andymic/rocksdb,wat-ze-hex/rocksdb,wlqGit/rocksdb,kaschaeffer/rocksdb,fengshao0907/rocksdb,NickCis/rocksdb,zhangpng/rocksdb,rDSN-Projects/rocksdb.replicated,JohnPJenkins/rocksdb,JoeWoo/rocksdb,RyanTech/rocksdb,zhangpng/rocksdb,norton/rocksdb,dkorolev/rocksdb,caijieming-baidu/rocksdb,alihalabyah/rocksdb,wlqGit/rocksdb,ylong/rocksdb,kaschaeffer/rocksdb,IMCG/RcoksDB,fengshao0907/rocksdb,zhangpng/rocksdb,vashstorm/rocksdb,biddyweb/rocksdb,jalexanderqed/rocksdb,makelivedotnet/rocksdb,fengshao0907/rocksdb,tsheasha/rocksdb,tsheasha/rocksdb,dkorolev/rocksdb,wskplho/rocksdb,vmx/rocksdb,tizzybec/rocksdb,siddhartharay007/rocksdb,sorphi/rocksdb,Vaisman/rocksdb,wat-ze-hex/rocksdb,JohnPJenkins/rocksdb,siddhartharay007/rocksdb,amyvmiwei/rocksdb,rDSN-Projects/rocksdb.replicated,SunguckLee/RocksDB,vmx/rocksdb,zhangpng/rocksdb,caijieming-baidu/rocksdb,bbiao/rocksdb,anagav/rocksdb,skunkwerks/rocksdb,sorphi/rocksdb,zhangpng/rocksdb,caijieming-baidu/rocksdb,RyanTech/rocksdb,caijieming-baidu/rocksdb,SunguckLee/RocksDB,SunguckLee/RocksDB,Andymic/rocksdb,ryneli/rocksdb,ylong/rocksdb,makelivedotnet/rocksdb,mbarbon/rocksdb,temicai/rocksdb,bbiao/rocksdb,OverlordQ/rocksdb,luckywhu/rocksdb,amyvmiwei/rocksdb,ryneli/rocksdb,geraldoandradee/rocksdb,JackLian/rocksdb,vashstorm/rocksdb,IMCG/RcoksDB,tizzybec/rocksdb,SunguckLee/RocksDB,sorphi/rocksdb,flabby/rocksdb,temicai/rocksdb,JohnPJenkins/rocksdb,ryneli/rocksdb,facebook/rocksdb,kaschaeffer/rocksdb,wat-ze-hex/rocksdb,jalexanderqed/rocksdb,jalexanderqed/rocksdb,dkorolev/rocksdb,caijieming-baidu/rocksdb,fengshao0907/rocksdb,virtdb/rocksdb,hobinyoon/rocksdb,tizzybec/rocksdb,RyanTech/rocksdb,JackLian/rocksdb,virtdb/rocksdb,rDSN-Projects/rocksdb.replicated,luckywhu/rocksdb,flabby/rocksdb,Vaisman/rocksdb,biddyweb/rocksdb,OverlordQ/rocksdb,zhangpng/rocksdb,JoeWoo/rocksdb,rDSN-Projects/rocksdb.replicated,siddhartharay007/rocksdb,virtdb/rocksdb,vmx/rocksdb,JoeWoo/rocksdb,wenduo/rocksdb,NickCis/rocksdb,skunkwerks/rocksdb,anagav/rocksdb,fengshao0907/rocksdb,Andymic/rocksdb,JohnPJenkins/rocksdb,JohnPJenkins/rocksdb,OverlordQ/rocksdb,wlqGit/rocksdb,tsheasha/rocksdb,mbarbon/rocksdb,virtdb/rocksdb,mbarbon/rocksdb,biddyweb/rocksdb,rDSN-Projects/rocksdb.replicated,SunguckLee/RocksDB,alihalabyah/rocksdb,norton/rocksdb,caijieming-baidu/rocksdb,norton/rocksdb,wlqGit/rocksdb,flabby/rocksdb,vmx/rocksdb,Applied-Duality/rocksdb,RyanTech/rocksdb,wskplho/rocksdb,ryneli/rocksdb,amyvmiwei/rocksdb,wat-ze-hex/rocksdb,NickCis/rocksdb,sorphi/rocksdb,wat-ze-hex/rocksdb,norton/rocksdb,bbiao/rocksdb,fengshao0907/rocksdb,vashstorm/rocksdb,wskplho/rocksdb,Applied-Duality/rocksdb,facebook/rocksdb,hobinyoon/rocksdb,IMCG/RcoksDB,fengshao0907/rocksdb,mbarbon/rocksdb,virtdb/rocksdb,luckywhu/rocksdb,biddyweb/rocksdb,anagav/rocksdb,jalexanderqed/rocksdb,makelivedotnet/rocksdb,JohnPJenkins/rocksdb,wlqGit/rocksdb,lgscofield/rocksdb,hobinyoon/rocksdb,Applied-Duality/rocksdb,ryneli/rocksdb,vashstorm/rocksdb,Andymic/rocksdb,tizzybec/rocksdb,tsheasha/rocksdb,siddhartharay007/rocksdb,Andymic/rocksdb,geraldoandradee/rocksdb,RyanTech/rocksdb,sorphi/rocksdb,mbarbon/rocksdb,alihalabyah/rocksdb,rDSN-Projects/rocksdb.replicated,Vaisman/rocksdb,facebook/rocksdb,siddhartharay007/rocksdb,temicai/rocksdb,luckywhu/rocksdb,lgscofield/rocksdb,OverlordQ/rocksdb,norton/rocksdb,JackLian/rocksdb,vashstorm/rocksdb,hobinyoon/rocksdb,kaschaeffer/rocksdb,dkorolev/rocksdb,dkorolev/rocksdb,ryneli/rocksdb,ylong/rocksdb,hobinyoon/rocksdb,Applied-Duality/rocksdb,alihalabyah/rocksdb,makelivedotnet/rocksdb,SunguckLee/RocksDB,alihalabyah/rocksdb,sorphi/rocksdb,wskplho/rocksdb,ryneli/rocksdb,makelivedotnet/rocksdb,wenduo/rocksdb,RyanTech/rocksdb,wskplho/rocksdb,Vaisman/rocksdb,JoeWoo/rocksdb,amyvmiwei/rocksdb,tsheasha/rocksdb,skunkwerks/rocksdb,NickCis/rocksdb,tsheasha/rocksdb,wenduo/rocksdb,jalexanderqed/rocksdb,temicai/rocksdb,wskplho/rocksdb,lgscofield/rocksdb,makelivedotnet/rocksdb,geraldoandradee/rocksdb,wskplho/rocksdb,facebook/rocksdb,alihalabyah/rocksdb,wenduo/rocksdb,siddhartharay007/rocksdb,vashstorm/rocksdb,facebook/rocksdb,NickCis/rocksdb,Applied-Duality/rocksdb,ylong/rocksdb,ylong/rocksdb,wlqGit/rocksdb,norton/rocksdb,wat-ze-hex/rocksdb,anagav/rocksdb,amyvmiwei/rocksdb,bbiao/rocksdb,tizzybec/rocksdb,hobinyoon/rocksdb,zhangpng/rocksdb