Fix utility naming issue

lib/hdprivatekey.js

@@ -337,10 +337,10 @@ HDPrivateKey.prototype._buildFromBuffers = function(arg) {
   var size = HDPrivateKey.ParentFingerPrintSize;
   var fingerPrint = Hash.sha256ripemd160(publicKey.toBuffer()).slice(0, size);
 
-  jsUtil.defineImmutable(this, {
+  JSUtil.defineImmutable(this, {
     xprivkey: xprivkey,
-    network: Network.get(bufferUtil.integerFromBuffer(arg.version)),
+    network: Network.get(BufferUtil.integerFromBuffer(arg.version)),
-    depth: bufferUtil.integerFromSingleByteBuffer(arg.depth),
+    depth: BufferUtil.integerFromSingleByteBuffer(arg.depth),
     privateKey: privateKey,
     publicKey: publicKey,
     fingerPrint: fingerPrint
@@ -349,7 +349,7 @@ HDPrivateKey.prototype._buildFromBuffers = function(arg) {
   var HDPublicKey = require('./hdpublickey');
   var hdPublicKey = new HDPublicKey(this);
 
-  jsUtil.defineImmutable(this, {
+  JSUtil.defineImmutable(this, {
     hdPublicKey: hdPublicKey,
     xpubkey: hdPublicKey.xpubkey
   });