Using ajv-formats with deno fails

Using `ajv-formats` with TypeScript+[deno](https://deno.land) (version 1.37.1) fails. I use the 'usual' idiom:

```
import addFormats from 'npm:ajv-formats':
.
.
.
addFormat(ajv);
```

and the compiler complains saying "This expression is not callable, [...]import [...] has no call signatures".

The same construction works with `node.js+tsc`.

I also looked at the `index.d.ts` file, as cached on my machine by deno, and it does not include any reference to `addFormat` at all, although the `index.js` file has it, but is not part of the exported `formatsPlugin` object.

Is this a deno bug or a bug with the distribution of `ajv-formats`?