Support a --require flag

## I'm submitting a...

[ ] Bug report  

[x] Feature request

## Current behavior

Currently, in order to run `@babel/node`, you have to include a plugin.

## Expected behavior

I would like to see a `--require` flag added to the CLI.

## Minimal reproduction of the problem with instructions

N/A

## What is the motivation/use case for changing the behavior?

We're now writing all of our JavaScript code using the `async`/`await` syntax in our JavaScript. This syntax will eventually be integrated into Node, but for now, we're using Babel. Many Node CLI tools include a `--require` flag that can be used to load modules directly from the command line, making it easy to add `@babel/register` to the project. There are also other ES6/ES7 niceties we're using that aren't currently supported by Node, and it's plausible there will be additional ones in the future.

This could be done with a plugin, but it strikes me as unnecessary when there's already a standardized solution to this problem. Plugins also require maintenance. For example, [db-migrate-plugin-babel](https://github.com/benjie/db-migrate-plugin-babel/blob/master/index.js#L11) is using the old `babel-node` instead of the new `@babel/register`. I'll submit an issue to that project, but that wouldn't be necessary with `--register`.

## Environment

db-migrate version: 0.10.2

db-migrate-pg: 0.2.5


Additional information:

- Node version: 9.2.0

- Platform: Linux (via node Docker image)

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