Update checkpoints.cpp

"hash": "0000000000090c594a09bf8ee830194fe6936e04c66226506a48f72e75f70171",
    "confirmations": 2,
    "size": 431,
    "height": 251423,
    "version": 2,
    "merkleroot": "a28e846a81b152319493763465aabb332021c5612274ffcb2c465c60da033cf0",
    "tx": [
        "99beb705a35859a815416725bb98aedc862eeee9202308412784978a2de82595",
        "789bcb93b13fc835c0ab27ad6fd2bbf2047b872b396838b430a4a2fc2d4204dc"
    ],
    "time": 1419076506,
    "nonce": 1006481659,
    "bits": "1b0e4512",
    "difficulty": 4592.56421717,
    "previousblockhash": "00000000000df7409359e38ef0280fa16529d44607a973a23dcf398acdaaa357",
    "nextblockhash": "00000000000bb1f34244fd79aae73e3f7dd32fe6f2da5e17d7432fae55dd4b5c"