Update crypto.md
Only documentation is changed: latin1 -> utf8
referred : https://github.com/nodejs/node/commit/b010c8716498dca398e61c388859fea92296feb3
function toBuf(str, encoding) {
if (typeof str === 'string') {
if (encoding === 'buffer' || !encoding)
encoding = 'utf8';
return new Buffer(str, encoding);
}
return str;
}