series of Nimble

【nimble】

　　series方法用于串行执行多个异步任务，通过npm可安装nimble。

　　Series works similarly to parallel, only it runs each function only once the previous has finished.

Again, you can add a final callback to use once all functions have completed.

　　

　　call参数是下Nimble传给我们的下一个方法的引用。

参考：http://caolan.github.io/nimble/