fix Checkpoints_tests: use peercoin checkpoints
fix Checkpoints_tests: use peercoin checkpoints

slimcoin-project/Slimcoin,BeirdoMud/MudCoin,slimcoin-project/Slimcoin,FuzzyBearBTC/peercoin,slimcoin-project/Slimcoin,BeirdoMud/MudCoin,BeirdoMud/MudCoin,bitgrowchain/bitgrow,bitgrowchain/bitgrow,BeirdoMud/MudCoin,FuzzyBearBTC/peercoin,FuzzyBearBTC/peercoin,FuzzyBearBTC/peercoin,slimcoin-project/Slimcoin,bitgrowchain/bitgrow,Peerapps/ppcoin,slimcoin-project/Slimcoin,Peerapps/ppcoin,slimcoin-project/Slimcoin,Peerapps/ppcoin,Peerapps/ppcoin,bitgrowchain/bitgrow