BIP32: Modified test vectors for hardened derivation with leading zeros

As mentioned in https://github.com/bitpay/bitcore-lib/issues/47, https://github.com/iancoleman/bip39/issues/58 and https://github.com/btcsuite/btcutil/issues/172, the private key with leading zeros(i.e. less than 32 bytes) should be padded to 32 bytes when we derive a hardened child private key from a private key. Unfortunately, the original test vector 3 is not suitable for this case since both keys are 32 bytes. In the new test vectors, the key m/0_H is 31 bytes. [btcsuite/btcutil

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