Changes the wallet passphrase from oldpassphrase to newpassphrase.
oldpassphrasestringREQUIREDnewpassphrasestringREQUIREDcurl --user myuser --data-binary '{"jsonrpc":"1.0","id":"1","method":"walletpassphrasechange","params":["old","new"]}' -H 'content-type:text/plain;' http://127.0.0.1:8332/null