Update the "fn get --help" CLI help text

[michael-w-williams]

The help text for "fn get --help" needs to be updated. Both "call" and "log" are no longer options for the command. So the text needs to updated as described below.

Here is the current text for "fn get --help":

fn get -   Get an object to retrieve its information

USAGE
fn [global options] get [command options] <subcommand>

DESCRIPTION
This command gets a 'call', 'configuration' or 'log' to retrieve information for an object ('app' or 'function').

SUBCOMMANDS
config, config, cf      Get configurations for apps and functions
help, h                 Shows a list of commands or help for one command

COMMAND OPTIONS
--help, -h  show help

FURTHER HELP:  See 'fn get <subcommand> --help' for more information about a command.

The text should be:

  fn get - Get an object to retrieve its information

USAGE
  fn [global options] get [command options] <subcommand>

DESCRIPTION
  This command gets the configuration information for an 'app' or 'function'.

SUBCOMMANDS
  config, cf      Get configurations for apps and functions
  help, h         Shows a list of commands or help for one command

COMMAND OPTIONS
  --help, -h  show help

FURTHER HELP:  See 'fn get <subcommand> --help' for more information about a command.

This issue was originially reported in: https://github.com/fnproject/docs/issues/120