Improving the visibility of one of the tables (#1306)

One of the tables has been fixed to look like all the other tables in the README

README.md

@@ -354,8 +354,8 @@ Courses | Duration | Effort | Prerequisites
 Courses | Duration | Effort | Prerequisites | Notes
 :-- | :--: | :--: | :--: | :--:
 [Computation Structures 1: Digital Circuits](https://learning.edx.org/course/course-v1:MITx+6.004.1x_3+3T2016) [alternative 1](https://ocw.mit.edu/courses/6-004-computation-structures-spring-2017/) [alternative 2](https://ocw.mit.edu/courses/6-004-computation-structures-spring-2009/) | 10 weeks | 6 hours/week | [Nand2Tetris II](https://www.coursera.org/learn/nand2tetris2) | Alternate links contain all 3 courses.
-[Computation Structures 2: Computer Architecture](https://learning.edx.org/course/course-v1:MITx+6.004.2x+3T2015) | 10 weeks | 6 hours/week | Computation Structures 1 |
-[Computation Structures 3: Computer Organization](https://learning.edx.org/course/course-v1:MITx+6.004.3x_2+1T2017) | 10 weeks | 6 hours/week | Computation Structures 2 |
+[Computation Structures 2: Computer Architecture](https://learning.edx.org/course/course-v1:MITx+6.004.2x+3T2015) | 10 weeks | 6 hours/week | Computation Structures 1 | - 
+[Computation Structures 3: Computer Organization](https://learning.edx.org/course/course-v1:MITx+6.004.3x_2+1T2017) | 10 weeks | 6 hours/week | Computation Structures 2 | -
 
 ### Advanced theory