fix double help printing

[rekram1-node]

fixes: #149

Now help messages won't show twice

Uses process.exit(1) as outlined in yargs docs:

import yargs from 'yargs'
const argv = yargs(process.argv.slice(2))
  .fail(function (msg, err, yargs) {
    if (err) throw err // preserve stack
    console.error('You broke it!')
    console.error(msg)
    console.error('You should be doing', yargs.help())
    process.exit(1)
  })
  .parse()