Missing `__esModule` marker

I'm trying to build an app with snowpack, that uses packages that were compiled with typescript with `esModuleInterop` on.

It seems like the interop functions injected by typescript think that poyfills are commonjs modules.

So for example if I have:

```javascript
import assert from 'assert'

assert(true)
```javascript

this gets compiled by typescript to

```javascript
const assert_1 = __importDefault(require("assert"));

assert_1.default(true)
```

and in the runtime assert_1 is
```javascript
{
default: {
default: assertFn,
}
}
```
the top-level default get inserted by `__importDefault`