fix core applications machine learning (#1143)

* Fix machine learning in core applications

The machine learning course is only 3 weeks long, not 11. Further, it's a very gentle introductory course. Even the prerequisite of Basic coding is stretching it, but it is as listed on the course page.

* Fix machine learning 

Machine learning should link to the entire specialization. The specialization is 11 weeks in all I believe, and they suggest 9 hours per week although that could be scaled down to 4-6 hours if you're just auditing. Also, the prerequisite should be basic coding, linear algebra is not necessary.

Closes #1118

README.md

@@ -296,7 +296,7 @@ Courses | Duration | Effort | Prerequisites | Discussion
 [Databases: Modeling and Theory](https://www.edx.org/course/modeling-and-theory)| 2 weeks | 10 hours/week | core programming | [chat](https://discord.gg/pMFqNf4)
 [Databases: Relational Databases and SQL](https://www.edx.org/course/databases-5-sql)| 2 weeks | 10 hours/week | core programming | [chat](https://discord.gg/P8SPPyF)
 [Databases: Semistructured Data](https://www.edx.org/course/semistructured-data)| 2 weeks | 10 hours/week | core programming | [chat](https://discord.gg/duCJ3GN)
-[Machine Learning](https://www.coursera.org/learn/machine-learning)| 11 weeks | 4-6 hours/week | linear algebra | [chat](https://discord.gg/NcXHDjy)
+[Machine Learning](https://www.coursera.org/specializations/machine-learning-introduction)| 11 weeks | 9 hours/week | Basic coding | [chat](https://discord.gg/NcXHDjy)
 [Computer Graphics](https://www.edx.org/course/computer-graphics-2)| 6 weeks | 12 hours/week | C++ or Java, linear algebra | [chat](https://discord.gg/68WqMNV)
 [Software Engineering: Introduction](https://www.edx.org/course/software-engineering-introduction) | 6 weeks | 8-10 hours/week | Core Programming, and a [sizable project](FAQ.md#why-require-experience-with-a-sizable-project-before-the-Software-Engineering-courses) | [chat](https://discord.gg/5Qtcwtz)