fix: stop running command with help or version flag

[haoranpb]

# cac/example
node help.js lint --help

help.js v0.0.0

Usage:
  $ help.js lint [...files]

Options:
  --type [type]  Choose a project type (default: node)
  --name <name>  Provide your name
  -h, --help     Display this message
  -v, --version  Display version number
[] { '--': [], type: 'node', h: true, help: true } <<-- command is still running

BTW, the showVersionOnExit and showHelpOnExit may also be outdated? Since they do not actually Exit anymore.

[codecov-io]

Codecov Report

Merging #64 into master will decrease coverage by 0.36%.
The diff coverage is 0%.

@@            Coverage Diff             @@
##           master      #64      +/-   ##
==========================================
- Coverage    67.3%   66.93%   -0.37%     
==========================================
  Files           6        6              
  Lines         367      369       +2     
  Branches       91       91              
==========================================
  Hits          247      247              
- Misses        117      119       +2     
  Partials        3        3

Impacted Files	Coverage Δ
src/CAC.ts	69.17% <0%> (-1.06%)	⬇️

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[egoist]

🎉 This PR is included in version 6.5.6 🎉

The release is available on:

• npm package (@latest dist-tag)
• GitHub release

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