Update requirements declaration of watchdog.
Update requirements declaration of watchdog.

According to their changelog the `watchmedo` utility is not installed by
default anymore.

bqbn/addons-server,mozilla/olympia,diox/olympia,bqbn/addons-server,diox/olympia,mozilla/addons-server,wagnerand/addons-server,wagnerand/addons-server,diox/olympia,mozilla/olympia,mozilla/addons-server,eviljeff/olympia,eviljeff/olympia,diox/olympia,bqbn/addons-server,eviljeff/olympia,bqbn/addons-server,wagnerand/addons-server,eviljeff/olympia,mozilla/addons-server,mozilla/olympia,mozilla/addons-server,wagnerand/addons-server,mozilla/olympia