textproc/highlight: unbreak on 9.x

./cli/main.cpp: In member function 'int HLCmdLineApp::run(int, const char**)':
./cli/main.cpp:406: error: 'unique_ptr' was not declared in this scope
./cli/main.cpp:406: error: expected primary-expression before '>' token
./cli/main.cpp:406: error: 'generator' was not declared in this scope

Reported by: pkg-fallout
Approved by: portmgr blanket