No order is guaranteed if migrations have the same date

## I'm submitting a...
- [x] Bug report
- [ ] Feature request
- [ ] Question

## Current behavior
Migrations on the same date (i.e. same year, month, day, hour, minute and second) aren't applied with any discernible criteria:


## Expected behavior
I would expect the alphabetical order to be respected.

## Minimal reproduction of the problem with instructions
create a bunch of migrations (if you have a machine fast enough to create multiple migrations on the same second, otherwise simply rename them)

for i in `seq 1 100`; do npx db_migrate create x$i --sql-file --env dev; done

apply them:

npx db_migrate up --env dev

watch them be in a randomish order

## What is the motivation / use case for changing the behavior?
Avoid the confusion of users and breakage when auto-generating migrations

## Environment

db-migrate version: 0.11.6

db-migrate driver with versions: pg 1.0.0


Additional information:

- Node version: v10.15.3

- Platform:  Linux (Ubuntu 18.04.3 LTS)

---
Want to back this issue? **[Post a bounty on it!](https://www.bountysource.com/issues/79518314-no-order-is-guaranteed-if-migrations-have-the-same-date?utm_campaign=plugin&utm_content=tracker%2F73887&utm_medium=issues&utm_source=github)** We accept bounties via [Bountysource](https://www.bountysource.com/?utm_campaign=plugin&utm_content=tracker%2F73887&utm_medium=issues&utm_source=github).