Fixed to the right functional code (typo)

Tested based on the following code:
1. You can easily to embrace some [parrallel] sub-tasks, just like this:
   --------------------------------------------------------------------
   var task = jsa.Task.wait(500).then(function() {
     jsa.Task.wait(500).then(function() {
       console.log('a'); 
     }).fire();
     jsa.Task.then(function(s) {
       jsa.Task.wait(300).then(function() {
         console.log('b' + s);
       }).fire();
     }).fire(10);
   }).then(function() {
     console.log('c');
   }).fire();
   --------------------------------------------------------------------
   You can run it to check if the result is "b10 a c".