hd: move nfkd to hd directory.

lib/hd/mnemonic.js

@@ -17,7 +17,7 @@ const BufferReader = require('../utils/reader');
 const encoding = require('../utils/encoding');
 const wordlist = require('./wordlist');
 const common = require('./common');
-const nfkd = require('../utils/nfkd');
+const nfkd = require('./nfkd');
 
 /*
  * Constants

lib/hd/nfkd-browser.js

@@ -6,7 +6,7 @@
 
 'use strict';
 
-const unorm = require('../../vendor/unorm');
+const unorm = require('./unorm');
 
 function nfkd(str) {
   if (str.normalize)