Update README.md

Author: yangyang14641

README.md

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 # ParallelProgrammingCourse
 Parallel programming course at Peking University
 
-![Yes We Code](https://octodex.github.com/images/baracktocat.png)
+![Yes We Code](https://octodex.github.com/images/baracktocat.jpg)
 
 ## Contents
 1. Homeworks and Projects