Typescript error when `postData` is missing

From the example:
```
const snippet = new HTTPSnippet({
method: 'GET',
url: 'http://mockbin.com/request',
});

const options = { indent: '\t' };
const output = snippet.convert('shell', 'curl', options);
console.log(output);
```

I get a typescript error

```
Argument of type '{ method: string; url: string; }' is not assignable to parameter of type 'HarRequest | HarEntry'.
Type '{ method: string; url: string; }' is not assignable to type 'HarRequest'.
Property 'postData' is missing in type '{ method: string; url: string; }' but required in type '{ postData: any; }'.ts(2345)
httpsnippet.d.ts(19, 5): 'postData' is declared here.
```

Start with the TypeScript declaration referenced in the error, httpsnippet.d.ts, and compare its HarRequest definition with the example that constructs HTTPSnippet without postData. Verify the corrected typing by compiling the shown example and confirming that the missing-postData error is gone.

索引モデルが issue の本文から書いたものです。