Keep separate GraphQL types as separate classes

Howdy!

I'm trying to generate Typescript types from an introspected GraphQL schema.

## What I did

I want to avoid combining similar classes, so I'm adding `--no-combine-classes`. My full command:

```sh
quicktype --src-lang graphql --lang typescript --graphql-schema schema.json --just-types --no-combine-classes query.json
```

## What I expected
The following combined class called `GridConfigClass` to be removed

```ts
export interface Grid {
config: GridConfigClass | null;
props: GridConfigClass | null;
}

export interface GridConfigClass {
items: Array;
}
```

and replaced with separate interfaces

```ts
export interface Grid {
config: GridConfig | null;
props: GridProps | null;
}

export interface GridConfig {
items: Array;
}

export interface GridProps {
items: Array;
}
```

## What happened
The output didn't change, and the combined `GridConfigClass` remains.

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Thanks for the awesome tool.