Added info about env SPOT_INVENTORY to --help

[bessarabov]

Tiny addition to --help. Now there is no info about env variable in --help:

$ spot --help
spot v0.9.1-0aa555f-2023-05-02T08:06:47Z
Usage:
  spot [command]

Application Options:
  -p, --file=       playbook file (default: spot.yml) [$SPOT_FILE]
  -t, --task=       task name
  -d, --target=     target name (default: default)
  -c, --concurrent= concurrent tasks (default: 1)
      --timeout=    ssh timeout (default: 30s)
  -i, --inventory=  inventory file or url
  -u, --user=       ssh user
  -k, --key=        ssh key
  -e, --env=        environment variables for all commands
      --skip=       skip commands
      --only=       run only commands
      --dry         dry run
  -v, --verbose     verbose mode
      --dbg         debug mode
  -h, --help        show help

Arguments:
  command:          run ad-hoc command on target hosts

This MR fixes it:

$ ~/git/spot/app/app --help
spot latest
Usage:
  app [command]

Application Options:
  -p, --playbook=   playbook file (default: spot.yml) [$SPOT_PLAYBOOK]
  -t, --task=       task name
  -d, --target=     target name (default: default)
  -c, --concurrent= concurrent tasks (default: 1)
      --timeout=    ssh timeout (default: 30s)
  -i, --inventory=  inventory file or url [$SPOT_INVENTORY]
  -u, --user=       ssh user
  -k, --key=        ssh key
  -e, --env=        environment variables for all commands
      --skip=       skip commands
      --only=       run only commands
      --dry         dry run
  -v, --verbose     verbose mode
      --dbg         debug mode
  -h, --help        show help

Arguments:
  command:          run ad-hoc command on target hosts

[coveralls]

Pull Request Test Coverage Report for Build 4865114018

• 0 of 0 changed or added relevant lines in 0 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage remained the same at 83.499%

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Totals
Change from base Build 4864692463:	0.0%
Covered Lines:	1174
Relevant Lines:	1406

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