lhc_travel --> lhc_booking

[peterpersiel]

abap-platform-rap110/exercises/ex03/README.md

Line 626 in 2e9482b

2. Also define the constant **`booking_status`** in the private section of the local handler class definition **`lhc_travel`**.

Also define the constant booking_status in the private section of the local handler class definition lhc_travel.

This should be corrected to lhc_booking instead.