[ts-to-oapi] Enums are not generated during conversion.

Hi. I have a number of TypeScript files which I am trying to generate OpenAPI documentation for using this tool. In one of the typescript files, I have an enum which looks like the following:

```ts
export enum SpeciesKind {
Human,
Bird,
Fish
}
```

I am using the following command to generate OpenAPI documentation from my typescript files:

```sh
npx typeconv -f ts -t oapi -o spec ./src/*.ts
```

When running the above command, everything is generated as expected except for any enums I have in my code, no OpenAPI schema is generated for them.