Switch Math for CS from OCW to OLL

Implement #832

Author: Alaharon123

README.md

@@ -208,7 +208,7 @@ In addition to their math elective, students must complete the following course
 
 Courses | Duration | Effort | Notes | Prerequisites | Discussion
 :-- | :--: | :--: | :--: | :--: | :--:
-[Mathematics for Computer Science](https://ocw.mit.edu/courses/electrical-engineering-and-computer-science/6-042j-mathematics-for-computer-science-spring-2015/index.htm) | 13 weeks | 5 hours/week | An alternate version with solutions to the problem sets is [here](https://ocw.mit.edu/courses/electrical-engineering-and-computer-science/6-042j-mathematics-for-computer-science-fall-2005/assignments/). Students struggling can consider the [Discrete Mathematics Specialization](https://www.coursera.org/specializations/discrete-mathematics) first. It is more interactive but less comprehensive, and costs money to unlock full interactivity. | Calculus 1C | [chat](https://discord.gg/EuTzNbF)
+[Mathematics for Computer Science](https://openlearninglibrary.mit.edu/courses/course-v1:OCW+6.042J+2T2019/about) ([alt](https://ocw.mit.edu/courses/electrical-engineering-and-computer-science/6-042j-mathematics-for-computer-science-spring-2015/index.htm)) | 13 weeks | 5 hours/week | An alternate version with solutions to the problem sets is [here](https://ocw.mit.edu/courses/electrical-engineering-and-computer-science/6-042j-mathematics-for-computer-science-fall-2005/assignments/). Students struggling can consider the [Discrete Mathematics Specialization](https://www.coursera.org/specializations/discrete-mathematics) first. It is more interactive but less comprehensive, and costs money to unlock full interactivity. | Calculus 1C | [chat](https://discord.gg/EuTzNbF)
 
 
 ### CS Tools