Improve xpub derivation perf by only deriving one node deep in loop

bench/index.js

@@ -99,7 +99,7 @@ options.forEach(options => {
 				break;
 
 			case 'xpub':
-				console.log(`Derivation Path: ${data.derivationPath}`);
+				console.log(`Derivation Index: ${data.index}`);
 				console.log(`xpub: ${data.xpub}`);
 				break;
 

src/key-formats/xpub.js

@@ -1,16 +1,14 @@
 const bitcoin = require('bitcoinjs-lib');
 
 const generateXpubKey = ({attempts, xpub}) => {
-	const change = 0;
 	const index = attempts - 1;
-	const derivationPath = `${change}/${index}`;
 
 	const node = bitcoin.bip32.fromBase58(xpub);
-	const {publicKey} = node.derivePath(derivationPath);
+	const {publicKey} = node.derive(index);
 
 	const format = () => ({
 		xpub,
-		derivationPath
+		index
 	});
 
 	return {publicKey, format};

test/vanity-addresses.js

@@ -97,7 +97,7 @@ testCases.forEach(options => {
 
 			case 'xpub': {
 				const node = bitcoin.bip32.fromBase58(keyData.xpub);
-				key = node.derivePath(keyData.derivationPath);
+				key = node.derive(keyData.index);
 				break;
 			}