[UPDATE] Update Coursera ML course (#843)

docs/机器学习/ML.en.md

@@ -14,9 +14,11 @@ The class is extremely friendly to novices, and Andrew has the ability to make m
 
 Of course, as a public mooc, the difficulty of this course has been deliberately lowered, and many mathematical derivations are skimmed over. If you are interested in machine learning theory and want to investigate the mathematical theory behind these algorithms, you can refer to [CS229](./CS229.md) and [CS189](./CS189.md).
 
+The new course is rebuilt into a specialization consisting of three courses.
+
 ## Course Resources
 
-- Course Website: <https://www.coursera.org/learn/machine-learning>
+- Course Website: <https://www.coursera.org/specializations/machine-learning-introduction>
 - Recordings: refer to the course website
 - Textbook: None
 - Assignments: refer to the course website

docs/机器学习/ML.md

@@ -14,9 +14,11 @@
 
 当然，这门课作为一个公开慕课，难度上刻意放低了些，很多数学推导大多一带而过，如果你有志于从事机器学习理论研究，想要深究这些算法背后的数学理论，可以参考 [CS229](./CS229.md) 和 [CS189](./CS189.md)。
 
+新版课程更新成了一个包含三个课程的系列，可以尝试在 Coursera 申请助学金后不用订阅即可学习。
+
 ## 课程资源
 
-- 课程网站：<https://www.coursera.org/learn/machine-learning>
+- 课程网站：<https://www.coursera.org/specializations/machine-learning-introduction>
 - 课程视频：参见课程网站
 - 课程教材：无
 - 课程作业：参见课程网站