c642bebeb7 fix typo in error message (Afounso Souza)
Pull request description:
The error message contains "do you have an hardened child number" but should be "do you have a hardened child number"
ACKs for top commit:
tcharding:
ACK c642bebeb7
apoelstra:
ACK c642bebeb7c452cdb81977f4fb9e36f2b1872be7; successfully ran local tests
Tree-SHA512: f8922d00a7bb687284387f880a1beeba6b1037d1885ea24c8162361880b250e6b44767c076ab40c6cd3cb9c667d28147413cc8257c46cd1383cc999c06735321