Update README.md

Author: alanedelman

README.md

@@ -45,9 +45,9 @@ By the end of the course students will be able to use Julia to write write porta
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 | 1  |   M  |  3/31     |      Edelman              |    Parallel Computing may not be what you think, top500, matmul vs matadd | [Intro](https://docs.google.com/presentation/d/1jkJqieNuWh4_Yx6Ura3xiGUc0NmaDK6a6J_zQJfQoEU/edit?usp=sharing)                                                                    |                                                                                                                              
 | 2  |   W  |  4/2     |      Edelman              | If you live with one programming language, you dont know what you are missing   | [Slides](https://docs.google.com/presentation/d/16Zf_SnDNlUmcCdqoaDeyAQmmqpxC66k646DCm3BXt1o/edit?usp=sharing)                                                                    |   
-| 3  |   F  |  4/4     |      Kimmerer              |  Allocations and other serial performance tips | [PerformantSerial Julia Pluto Notebook](https://mitmath.github.io/Parallel-Computing-Spoke/notebooks/PerformantSerialJulia.html)                                                                    |   
+| 3  |   F  |  4/4     |      Kimmerer              |  Allocations and other serial performance tips | | [PerformantSerial Julia Pluto Notebook](https://mitmath.github.io/Parallel-Computing-Spoke/notebooks/PerformantSerialJulia.html)                                                                    |   
 ### Week 2 - Parallelism Concepts and Julia Performance
-| 4 |   M  |  4/7    |      Edelman              |   Parallel Prefix | |    
+| 4 |   M  |  4/7    |      Edelman              |   Parallel Prefix |     
 ### Week 3 - Multithreading and Multitasking
 
 ### Week 4 - GPU Computing