Fix typo in configMAX_PRIORITIES (#109)

Author: CodesOtakuYT

ch04.md

@@ -632,7 +632,7 @@ select the *Running* state task and the maximum allowable value for
 ### 4.5.1 Generic Scheduler
 
 The generic scheduler is written in C and can be used with all FreeRTOS
-architecture ports. It does not impose an upper limit on `configMAX_PRIORITEIS`.
+architecture ports. It does not impose an upper limit on `configMAX_PRIORITIES`.
 In general, it is advisable to minimize `configMAX_PRIORITIES` because more
 values require more RAM and will result in a longer worst-case execution time.