Invalid TS generated from ST

Using:

```
typeconv 1.7.0
node v17.4.0
```

input.ts

```ts
export type T = number | string;
```

And on the command line:

```
npx typeconv -f ts -t st -o out input.ts
```

Gives a file `out/input.ts` that contains this invalid import declaration:

```ts
import { suretype as , v as , compile as } from 'suretype';
```

The generated import declaration should be:

```ts
import { suretype, v, compile} from 'suretype';
```