docs(set): edit weakmap

docs/generator-async.md

@@ -320,7 +320,7 @@ var Thunk = function(fn){
 };
 
 // ES6版本
-var Thunk = function(fn) {
+const Thunk = function(fn) {
   return function (...args) {
     return function (callback) {
       return fn.call(this, ...args, callback);
@@ -342,10 +342,9 @@ readFileThunk(fileA)(callback);
 function f(a, cb) {
   cb(a);
 }
-let ft = Thunk(f);
+const ft = Thunk(f);
 
-let log = console.log.bind(console);
-ft(1)(log) // 1
+ft(1)(console.log) // 1
 ```
 
 ### Thunkify 模块

docs/set-map.md

@@ -1014,7 +1014,7 @@ undefined
 > let wm = new WeakMap();
 undefined
 
-> const b = new Object();
+> let b = new Object();
 undefined
 
 > global.gc();
@@ -1053,7 +1053,7 @@ undefined
 
 // 解除 b 的引用以后，heapUsed 变回 4M 左右
 // 说明 WeakMap 中的那个长度为 5*1024*1024 的数组被销毁了
-> process.memoryUsage(); 
+> process.memoryUsage();
 { rss: 20639744,
   heapTotal: 8425472,
   heapUsed: 3979792,