Lab 4 - Missing include

[rbuenviaje]

Seems like #include "semphr.h" needs to be added to aws_hello_world.c or I receive errors when adding SemaphoreHandle_t xSemaphore; in https://github.com/rpcme/afr-workshop-cc3220sf/blob/master/Lab4.md#initialize-the-mutex-semaphore

[rpcme]

This was fixed during the workshop to the end of the section "The Accelerometer Task".