doc: Correcting variable name in example [ci skip]
doc: Correcting variable name in example [ci skip]

flightaware/cpp-driver,mikefero/cpp-driver,datastax/cpp-driver,flightaware/cpp-driver,mikefero/cpp-driver,datastax/cpp-driver,mikefero/cpp-driver,hpcc-systems/cpp-driver,hpcc-systems/cpp-driver,datastax/cpp-driver,hpcc-systems/cpp-driver,datastax/cpp-driver,flightaware/cpp-driver,mikefero/cpp-driver,mikefero/cpp-driver,flightaware/cpp-driver,hpcc-systems/cpp-driver