Escape doesn't escape anything at all when using double quotes

https://github.com/db-migrate/db-migrate-base/blob/05762f395e43643c2e9a1641e7b2a9492f34ae5a/index.js#L682

```js
return str.replace(/"/g, '"');
```

The replacement string was probably meant to be `'\\"'`.

The code should be

```js
return str.replace(/\\/g, '\\\\').replace(/"/g, '\\"');
```

---
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