Change the directory of Bootstrap from '_assets' to static 'assets'.

assets/vendor/bootstrap/grunt/bs-raw-files-generator.js

@@ -0,0 +1,31 @@
+/* global btoa: true */
+/*!
+ * Bootstrap Grunt task for generating raw-files.min.js for the Customizer
+ * http://getbootstrap.com
+ * Copyright 2014 Twitter, Inc.
+ * Licensed under MIT (https://github.com/twbs/bootstrap/blob/master/LICENSE)
+ */
+'use strict';
+var btoa = require('btoa');
+var fs = require('fs');
+
+function getFiles(type) {
+  var files = {};
+  fs.readdirSync(type)
+    .filter(function (path) {
+      return type === 'fonts' ? true : new RegExp('\\.' + type + '$').test(path);
+    })
+    .forEach(function (path) {
+      var fullPath = type + '/' + path;
+      files[path] = (type === 'fonts' ? btoa(fs.readFileSync(fullPath)) : fs.readFileSync(fullPath, 'utf8'));
+    });
+  return 'var __' + type + ' = ' + JSON.stringify(files) + '\n';
+}
+
+module.exports = function generateRawFilesJs(banner) {
+  if (!banner) {
+    banner = '';
+  }
+  var files = banner + getFiles('js') + getFiles('less') + getFiles('fonts');
+  fs.writeFileSync('docs/assets/js/raw-files.min.js', files);
+};