gitignore: add *.dat
gitignore: add *.dat

Github-Pull: #15809
Rebased-From: e7acf44bbfd05233f7753b3c8230892196facde8

untrustbank/litecoin,ahmedbodi/vertcoin,GroestlCoin/GroestlCoin,bespike/litecoin,myriadteam/myriadcoin,qtumproject/qtum,GroestlCoin/bitcoin,qtumproject/qtum,GroestlCoin/GroestlCoin,OmniLayer/omnicore,OmniLayer/omnicore,qtumproject/qtum,GroestlCoin/GroestlCoin,myriadteam/myriadcoin,OmniLayer/omnicore,myriadcoin/myriadcoin,GroestlCoin/bitcoin,vertcoin/vertcoin,vertcoin/vertcoin,bespike/litecoin,vertcoin/vertcoin,bespike/litecoin,untrustbank/litecoin,bespike/litecoin,GroestlCoin/GroestlCoin,bespike/litecoin,myriadcoin/myriadcoin,untrustbank/litecoin,myriadcoin/myriadcoin,OmniLayer/omnicore,ahmedbodi/vertcoin,GroestlCoin/bitcoin,vertcoin/vertcoin,untrustbank/litecoin,GroestlCoin/GroestlCoin,myriadcoin/myriadcoin,bespike/litecoin,ahmedbodi/vertcoin,qtumproject/qtum,OmniLayer/omnicore,myriadteam/myriadcoin,myriadcoin/myriadcoin,ahmedbodi/vertcoin,untrustbank/litecoin,myriadteam/myriadcoin,qtumproject/qtum,ahmedbodi/vertcoin,GroestlCoin/bitcoin,qtumproject/qtum,GroestlCoin/bitcoin,GroestlCoin/GroestlCoin,myriadteam/myriadcoin,ahmedbodi/vertcoin,myriadteam/myriadcoin,GroestlCoin/bitcoin,myriadcoin/myriadcoin,vertcoin/vertcoin,vertcoin/vertcoin,OmniLayer/omnicore,untrustbank/litecoin,qtumproject/qtum