Merge pull request #130 from Ad7amstein/master

Update Math Course Links from OpenLearningLibrary to MITx Online

Resolves #131

Author: waciumawanjohi

README.md

@@ -132,11 +132,11 @@ _The Algorithms courses are taught in Java. If students need to learn Java, they
 
 ### Single Variable Calculus
 
-[Calculus 1A: Differentiation](https://openlearninglibrary.mit.edu/courses/course-v1:MITx+18.01.1x+2T2019/about)
+[Calculus 1A: Differentiation](https://mitxonline.mit.edu/courses/course-v1:MITxT+18.01.1x/)
 
-[Calculus 1B: Integration](https://openlearninglibrary.mit.edu/courses/course-v1:MITx+18.01.2x+3T2019/about)
+[Calculus 1B: Integration](https://mitxonline.mit.edu/courses/course-v1:MITxT+18.01.2x/)
 
-[Calculus 1C: Coordinate Systems & Infinite Series](https://openlearninglibrary.mit.edu/courses/course-v1:MITx+18.01.3x+1T2020/about)
+[Calculus 1C: Coordinate Systems & Infinite Series](https://mitxonline.mit.edu/courses/course-v1:MITxT+18.01.3x/)
 
 ### Linear Algebra