Fix: config.pool default min may greater than user's config max

[chenhui5416]

use case:

  const knex = require('knex')({
    pool: {max: 1}
  })

Now, knex would thorw error, while pool max should greater than min.

[elhigu]

Hi, thanks for the pull request. There is linting error and the test case for this is missing.

I think it would be better to just throw error if min > max in that way there wouldn't be any hidden functionality which will hide clearly invalid configuration.

Now if you pass { max: 2, min: 10 } to pool, automatic changing min -> 2 will hide this configuration fail, where you probably wanted to pass { min: 2, max: 10 } instead.

[elhigu]

Just throwing an error because of invalid configuration is better than trying to automatically fix config. Also automatic test case is required.

[elhigu]

Closing for now, can be reopened if implementation is fixed and test case added.