wrong formatted db-migrate db command should error out

## I'm submitting a...

- [x] Bug report
- [ ] Feature request
- [ ] Question

## Current behavior
Running `db-migrate db create mydb` hangs. Note the missing colon.

## Expected behavior
Error message like 'Unknown command db' or 'Did you mean db:create ?'

## Minimal reproduction of the problem with instructions
Run `db-migrate db create mydb`. I'm using postgres if that matters.

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

## Environment

db-migrate version: ^0.10.6

db-migrate driver with versions: db-migrate-pg ^0.3.1


Additional information:

- Node version: v9.4.0

- Platform:  Mac

Others:

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