images.testing-docs: decapitalize "listener" for consistency
images.testing-docs: decapitalize "listener" for consistency

This was the only document that had "Listener" starting with capital "L".

AlexIljin/factor,tgunr/factor,AlexIljin/factor,bpollack/factor,AlexIljin/factor,bpollack/factor,tgunr/factor,tgunr/factor,bpollack/factor,mrjbq7/factor,mrjbq7/factor,factor/factor,AlexIljin/factor,tgunr/factor,mrjbq7/factor,factor/factor,factor/factor,tgunr/factor,factor/factor,mrjbq7/factor,bpollack/factor,AlexIljin/factor,bpollack/factor,bpollack/factor,mrjbq7/factor,AlexIljin/factor,AlexIljin/factor,factor/factor,bpollack/factor,tgunr/factor,factor/factor,mrjbq7/factor