correct grammar in include/FreeRTOS.h
correct grammar in include/FreeRTOS.h

Co-authored-by: Aniruddha Kanhere <b3fd640b9b0094a1c4214c7e38f832dc09fa7aaa@users.noreply.github.com>
FreeRTOS/FreeRTOS-Kernel,FreeRTOS/FreeRTOS-Kernel