fix(cli): command executed twice on error

[rfratto]

Running tk show with no arguments would print the help text twice, like so:

Error: accepts 1 arg(s), received 0
Usage:
  tk show [directory] [flags]

Flags:
  -h, --help             help for show
  -t, --target strings   only use the specified objects (Format: <type>/<name>)

Global Flags:
  -v, --verbose

Error: accepts 1 arg(s), received 0
Usage:
  tk show [directory] [flags]

Flags:
  -h, --help             help for show
  -t, --target strings   only use the specified objects (Format: <type>/<name>)

Global Flags:
  -v, --verbose

Ouch: accepts 1 arg(s), received 0

This PR fixes the repeated output.

[sh0rez]

LGTM