Update free-programming-books.md (EbookFoundation#2965)

Author: akan01n

free-programming-books.md

@@ -629,7 +629,7 @@
 * [Is Parallel Programming Hard, And, If So, What Can You Do About It?](https://www.kernel.org/pub/linux/kernel/people/paulmck/perfbook/perfbook.html) - Paul E. McKenney
 * [Programming on Parallel Machines; GPU, Multicore, Clusters and More](http://heather.cs.ucdavis.edu/parprocbook) - Norm Matloff
 Kerridge (PDF) (email address *requested*, not required)
-* [The OpenCL Programming Book](https://www.fixstars.com/en/opencl/book/OpenCLProgrammingBook/contents/)
+* [The OpenCL Programming Book](https://us.fixstars.com/opencl/book/OpenCLProgrammingBook/contents/)
 * [Using Concurrency and Parallelism Effectively – I](http://bookboon.com/en/using-concurrency-and-parallelism-effectively-i-ebook) - Jon Kerridge (PDF) (email address *requested*, not required)
 * [Using Concurrency and Parallelism Effectively – II](http://bookboon.com/en/using-concurrency-and-parallelism-effectively-ii-ebook) - Jon