Use ltub for litecoin by default instead of xprv

Introduced when upgrading from bitcoinjs-lib v3.3.0

src/js/bitcoinjs-extensions.js

@@ -316,3 +316,14 @@ bitcoinjs.bitcoin.networks.litecoinBip49 = {
     scriptHash: 0x32,
     wif: 0xb0
 };
+
+bitcoinjs.bitcoin.networks.litecoinXprv = {
+    messagePrefix: '\x19Litecoin Signed Message:\n',
+    bip32: {
+      public: 0x0488b21e,
+      private: 0x0488ade4,
+    },
+    pubKeyHash: 0x30,
+    scriptHash: 0x32,
+    wif: 0xb0
+};