[doc] fix Makefile target in benchmarking.md
[doc] fix Makefile target in benchmarking.md

while the resulting binary is called `bench_bitcoin`, the Makefile target is
named `bitcoin_bench` (see `src/Makefile.bench.include`)

yenliangl/bitcoin,apoelstra/bitcoin,monacoinproject/monacoin,fujicoin/fujicoin,bitcoinsSG/bitcoin,jambolo/bitcoin,jamesob/bitcoin,mruddy/bitcoin,jlopp/statoshi,domob1812/bitcoin,kallewoof/bitcoin,ElementsProject/elements,ajtowns/bitcoin,bitcoinsSG/bitcoin,alecalve/bitcoin,EthanHeilman/bitcoin,dscotese/bitcoin,n1bor/bitcoin,prusnak/bitcoin,MeshCollider/bitcoin,jonasschnelli/bitcoin,dscotese/bitcoin,tecnovert/particl-core,GroestlCoin/GroestlCoin,JeremyRubin/bitcoin,jonasschnelli/bitcoin,jnewbery/bitcoin,practicalswift/bitcoin,achow101/bitcoin,qtumproject/qtum,Xekyo/bitcoin,jambolo/bitcoin,jambolo/bitcoin,GroestlCoin/GroestlCoin,n1bor/bitcoin,rnicoll/dogecoin,sipsorcery/bitcoin,mruddy/bitcoin,alecalve/bitcoin,particl/particl-core,sstone/bitcoin,anditto/bitcoin,mm-s/bitcoin,jlopp/statoshi,jnewbery/bitcoin,litecoin-project/litecoin,mm-s/bitcoin,achow101/bitcoin,gjhiggins/vcoincore,vertcoin/vertcoin,instagibbs/bitcoin,rnicoll/dogecoin,namecoin/namecoin-core,prusnak/bitcoin,pataquets/namecoin-core,sipsorcery/bitcoin,tjps/bitcoin,sipsorcery/bitcoin,andreaskern/bitcoin,sstone/bitcoin,prusnak/bitcoin,vertcoin/vertcoin,tecnovert/particl-core,ElementsProject/elements,andreaskern/bitcoin,namecoin/namecoin-core,fanquake/bitcoin,lateminer/bitcoin,vertcoin/vertcoin,vertcoin/vertcoin,JeremyRubin/bitcoin,MeshCollider/bitcoin,jlopp/statoshi,gjhiggins/vcoincore,AkioNak/bitcoin,MarcoFalke/bitcoin,Xekyo/bitcoin,GroestlCoin/GroestlCoin,tjps/bitcoin,fujicoin/fujicoin,dscotese/bitcoin,midnightmagic/bitcoin,monacoinproject/monacoin,jnewbery/bitcoin,qtumproject/qtum,kallewoof/bitcoin,sstone/bitcoin,DigitalPandacoin/pandacoin,cdecker/bitcoin,jambolo/bitcoin,qtumproject/qtum,mitchellcash/bitcoin,anditto/bitcoin,GroestlCoin/GroestlCoin,practicalswift/bitcoin,particl/particl-core,fujicoin/fujicoin,jlopp/statoshi,anditto/bitcoin,namecoin/namecoin-core,MarcoFalke/bitcoin,sstone/bitcoin,peercoin/peercoin,vertcoin/vertcoin,monacoinproject/monacoin,ajtowns/bitcoin,cdecker/bitcoin,bitcoinknots/bitcoin,qtumproject/qtum,fanquake/bitcoin,prusnak/bitcoin,monacoinproject/monacoin,pstratem/bitcoin,DigitalPandacoin/pandacoin,tjps/bitcoin,instagibbs/bitcoin,Xekyo/bitcoin,ElementsProject/elements,tjps/bitcoin,pataquets/namecoin-core,alecalve/bitcoin,yenliangl/bitcoin,EthanHeilman/bitcoin,Xekyo/bitcoin,jonasschnelli/bitcoin,tecnovert/particl-core,midnightmagic/bitcoin,apoelstra/bitcoin,tjps/bitcoin,MeshCollider/bitcoin,bitcoin/bitcoin,apoelstra/bitcoin,n1bor/bitcoin,EthanHeilman/bitcoin,yenliangl/bitcoin,andreaskern/bitcoin,anditto/bitcoin,sipsorcery/bitcoin,MarcoFalke/bitcoin,dscotese/bitcoin,mruddy/bitcoin,namecoin/namecore,jambolo/bitcoin,sstone/bitcoin,gjhiggins/vcoincore,kallewoof/bitcoin,tecnovert/particl-core,midnightmagic/bitcoin,ahmedbodi/vertcoin,andreaskern/bitcoin,bitcoin/bitcoin,pataquets/namecoin-core,peercoin/peercoin,yenliangl/bitcoin,namecoin/namecoin-core,mitchellcash/bitcoin,achow101/bitcoin,fujicoin/fujicoin,bitcoinknots/bitcoin,jnewbery/bitcoin,MarcoFalke/bitcoin,midnightmagic/bitcoin,jambolo/bitcoin,alecalve/bitcoin,GroestlCoin/bitcoin,pataquets/namecoin-core,ahmedbodi/vertcoin,jamesob/bitcoin,EthanHeilman/bitcoin,domob1812/bitcoin,domob1812/namecore,JeremyRubin/bitcoin,litecoin-project/litecoin,mitchellcash/bitcoin,pstratem/bitcoin,andreaskern/bitcoin,ElementsProject/elements,DigitalPandacoin/pandacoin,ahmedbodi/vertcoin,pstratem/bitcoin,mitchellcash/bitcoin,domob1812/namecore,instagibbs/bitcoin,tecnovert/particl-core,ajtowns/bitcoin,apoelstra/bitcoin,Sjors/bitcoin,GroestlCoin/GroestlCoin,dscotese/bitcoin,GroestlCoin/bitcoin,mruddy/bitcoin,tecnovert/particl-core,litecoin-project/litecoin,litecoin-project/litecoin,monacoinproject/monacoin,jnewbery/bitcoin,JeremyRubin/bitcoin,bitcoin/bitcoin,fujicoin/fujicoin,domob1812/namecore,bitcoinsSG/bitcoin,rnicoll/bitcoin,MeshCollider/bitcoin,instagibbs/bitcoin,AkioNak/bitcoin,peercoin/peercoin,cdecker/bitcoin,sipsorcery/bitcoin,yenliangl/bitcoin,prusnak/bitcoin,mruddy/bitcoin,cdecker/bitcoin,dscotese/bitcoin,domob1812/bitcoin,n1bor/bitcoin,bitcoinknots/bitcoin,Sjors/bitcoin,gjhiggins/vcoincore,kallewoof/bitcoin,rnicoll/bitcoin,GroestlCoin/bitcoin,anditto/bitcoin,ajtowns/bitcoin,peercoin/peercoin,bitcoinsSG/bitcoin,jonasschnelli/bitcoin,andreaskern/bitcoin,mitchellcash/bitcoin,vertcoin/vertcoin,gjhiggins/vcoincore,namecoin/namecoin-core,GroestlCoin/GroestlCoin,domob1812/bitcoin,AkioNak/bitcoin,mm-s/bitcoin,midnightmagic/bitcoin,prusnak/bitcoin,Xekyo/bitcoin,DigitalPandacoin/pandacoin,namecoin/namecore,apoelstra/bitcoin,AkioNak/bitcoin,mruddy/bitcoin,MarcoFalke/bitcoin,ahmedbodi/vertcoin,fanquake/bitcoin,jamesob/bitcoin,MeshCollider/bitcoin,rnicoll/dogecoin,domob1812/namecore,Sjors/bitcoin,qtumproject/qtum,bitcoinknots/bitcoin,DigitalPandacoin/pandacoin,JeremyRubin/bitcoin,GroestlCoin/bitcoin,particl/particl-core,sstone/bitcoin,pstratem/bitcoin,namecoin/namecoin-core,fujicoin/fujicoin,bitcoin/bitcoin,ElementsProject/elements,MarcoFalke/bitcoin,mm-s/bitcoin,rnicoll/dogecoin,Sjors/bitcoin,monacoinproject/monacoin,AkioNak/bitcoin,sipsorcery/bitcoin,n1bor/bitcoin,GroestlCoin/bitcoin,EthanHeilman/bitcoin,rnicoll/bitcoin,practicalswift/bitcoin,instagibbs/bitcoin,mitchellcash/bitcoin,Sjors/bitcoin,namecoin/namecore,rnicoll/bitcoin,practicalswift/bitcoin,litecoin-project/litecoin,jlopp/statoshi,jamesob/bitcoin,rnicoll/bitcoin,peercoin/peercoin,ajtowns/bitcoin,pstratem/bitcoin,ElementsProject/elements,fanquake/bitcoin,particl/particl-core,bitcoinsSG/bitcoin,qtumproject/qtum,lateminer/bitcoin,achow101/bitcoin,cdecker/bitcoin,domob1812/bitcoin,ahmedbodi/vertcoin,achow101/bitcoin,pataquets/namecoin-core,MeshCollider/bitcoin,peercoin/peercoin,jlopp/statoshi,EthanHeilman/bitcoin,litecoin-project/litecoin,namecoin/namecore,namecoin/namecore,kallewoof/bitcoin,rnicoll/dogecoin,midnightmagic/bitcoin,practicalswift/bitcoin,kallewoof/bitcoin,bitcoinsSG/bitcoin,pataquets/namecoin-core,qtumproject/qtum,fanquake/bitcoin,pstratem/bitcoin,domob1812/bitcoin,lateminer/bitcoin,n1bor/bitcoin,bitcoin/bitcoin,Xekyo/bitcoin,jonasschnelli/bitcoin,namecoin/namecore,lateminer/bitcoin,yenliangl/bitcoin,alecalve/bitcoin,mm-s/bitcoin,AkioNak/bitcoin,domob1812/namecore,GroestlCoin/bitcoin,lateminer/bitcoin,gjhiggins/vcoincore,alecalve/bitcoin,anditto/bitcoin,ahmedbodi/vertcoin,cdecker/bitcoin,instagibbs/bitcoin,ajtowns/bitcoin,bitcoinknots/bitcoin,practicalswift/bitcoin,rnicoll/bitcoin,mm-s/bitcoin,apoelstra/bitcoin,domob1812/namecore,jamesob/bitcoin,bitcoin/bitcoin,JeremyRubin/bitcoin,achow101/bitcoin,lateminer/bitcoin,jamesob/bitcoin,DigitalPandacoin/pandacoin,tjps/bitcoin,particl/particl-core,particl/particl-core,fanquake/bitcoin