Fix help command usage string
Fix help command usage string

The information in the usage string for the `help` command about
how to get more information about a specific command was incorrect:

"influxd help [command]" does not work, but "influxd [command] --help"
does.

linearb/influxdb,influxdb/influxdb,influxdb/influxdb,mark-rushakoff/influxdb,mnuessler/influxdb,pkittenis/influxdb,jgeiger/influxdb,nooproblem/influxdb,influxdb/influxdb,influxdb/influxdb,li-ang/influxdb,jgeiger/influxdb,mark-rushakoff/influxdb,otoolep/influxdb,otoolep/influxdb,otoolep/influxdb,nooproblem/influxdb,archsaber/influxdb,nooproblem/influxdb,vladlopes/influxdb,linearb/influxdb,jgeiger/influxdb,jgeiger/influxdb,nooproblem/influxdb,mark-rushakoff/influxdb,mnuessler/influxdb,pkittenis/influxdb,runner-mei/influxdb,chenziliang/influxdb,mnuessler/influxdb,benbjohnson/influxdb,vladlopes/influxdb,vladlopes/influxdb,mnuessler/influxdb,influxdb/influxdb,vladlopes/influxdb,mark-rushakoff/influxdb,pkittenis/influxdb,benbjohnson/influxdb,benbjohnson/influxdb,benbjohnson/influxdb,archsaber/influxdb,pkittenis/influxdb,linearb/influxdb,jgeiger/influxdb,mnuessler/influxdb,chenziliang/influxdb,otoolep/influxdb,jgeiger/influxdb,pkittenis/influxdb,runner-mei/influxdb,chenziliang/influxdb,li-ang/influxdb,pkittenis/influxdb,influxdb/influxdb,archsaber/influxdb,mark-rushakoff/influxdb,mnuessler/influxdb,influxdata/influxdb,archsaber/influxdb,runner-mei/influxdb,nooproblem/influxdb,runner-mei/influxdb,influxdata/influxdb,mark-rushakoff/influxdb,linearb/influxdb,chenziliang/influxdb,otoolep/influxdb,otoolep/influxdb,linearb/influxdb