Update _toc.yml

Author: liamjberrisford

_toc.yml

@@ -258,7 +258,7 @@ parts:
                 sections:
                   - file: individual_modules/parallel_computing/architecture_and_concurrency
                   - file: individual_modules/parallel_computing/multithreading_io
-                  - file: individual_modules/parallel_computing/multiprocessing_fractal
+                  - file: individual_modules/parallel_computing/multiprocessing_cpu
                   - file: individual_modules/parallel_computing/mpi_hello_world
                   - file: individual_modules/parallel_computing/mpi_simple_communication
                   - file: individual_modules/parallel_computing/mpi_collective_comms