debug.go using fmt.Sprintf incorrectly

right now, it prints:
  DEBUG: watch [/service1 http://127.0.0.1:4001] [%!s(MISSING)]

update below:
fmt.Sprintf(f, args)        ---------->      fmt.Sprintf(f, args...)

then it's ok:
 DEBUG: get /service1 [http://127.0.0.1:4001]