Published package is missing type declarations

### [REQUIRED] Environment info

**firebase-tools:** 8.4.3

**Platform:** macOS Catalina

### [REQUIRED] Test case

```ts
import * as firebaseTools from 'firebase-tools'
```

or

```ts
import firebaseTools from 'firebase-tools'
```

### [REQUIRED] Steps to reproduce

Just import the 'firebase-tools' module in a TypeScript file and run `tsc` on it.

### [REQUIRED] Expected behavior

It should come with its own types (it is written in TypeScript, after all).

### [REQUIRED] Actual behavior

TypeScript complains that this module has no type declations:

```
Could not find a declaration file for module 'firebase-tools'. '/node_modules/firebase-tools/lib/index.js' implicitly has an 'any' type.
Try `npm install @types/firebase-tools` if it exists or add a new declaration (.d.ts) file containing `declare module 'firebase-tools';`
```

Sure enough, looking at the actual published package in my `node_modules`, it contains no `.d.ts` files. Why?

There's also nothing at `@types/firebase-tools`.