refactor: drop lodash for lib/hexo/index.js (#3845)

* refactor: drop lodash.cloneDeep for lib/hexo/index.js
* refactor: drop lodash.debounce for lib/hexo/index.js

lib/hexo/index.js

@@ -28,8 +28,6 @@ const resolve = require('resolve');
 const full_url_for = require('../plugins/helper/full_url_for');
 const { inherits } = require('util');
 
-const { cloneDeep, debounce } = _;
-
 const libDir = dirname(__dirname);
 const dbVersion = 1;
 
@@ -73,6 +71,20 @@ const createLoadThemeRoute = function(generatorResult, locals, ctx) {
   };
 };
 
+function debounce(func, wait, immediate) {
+  let timeout;
+  return function() {
+    const context = this;
+    const args = arguments;
+    clearTimeout(timeout);
+    timeout = setTimeout(() => {
+      timeout = null;
+      if (!immediate) func.apply(context, args);
+    }, wait);
+    if (immediate && !timeout) func.apply(context, args);
+  };
+}
+
 class Hexo {
   constructor(base = process.cwd(), args = {}) {
     Reflect.apply(EventEmitter, this, []);
@@ -109,7 +121,7 @@ class Hexo {
       tag: new extend.Tag()
     };
 
-    this.config = cloneDeep(defaultConfig);
+    this.config = Object.assign({}, defaultConfig);
 
     this.log = logger(this.env);