Memory-leak if we call db.close() right after new SnapDB() without db.ready()

[huan]

According to the fix of #2, I believe we also need to put some code inside the close() function.

The following code will demonstrate that the node program will hang.

#!/usr/bin/env ts-node

import {
  SnapDB,
}               from 'snap-db'

async function main () {
  const db = new SnapDB({
    dir: '/tmp/xx',
    key: 'string',
  })
  // await db.ready()
  await db.close()
  console.info('DB close-ed')
}

main()

If we uncomment the await db.ready() in the code, then everything will ok.

[only-cliches]

1.1.2 is now live on NPM, this issue has been resolved. Feel free to comment if you find anything further!

[huan]

Thanks for the fix!