Can't import package in Swift Playgrounds

### Step 0: Are you in the right place?

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file a Github issue.
* If this is a __feature request__ please use the Feature Request template.
* For general technical questions, post a question on [StackOverflow](http://stackoverflow.com/)
with the `firebase` tag.
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* Once you've read this section and determined that your issue is appropriate for
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### [REQUIRED] Step 1: Describe your environment

* Xcode version: Swift Playgrounds
* Firebase SDK version: Latest
* Installation method: `Swift Package Manager` (select one)
* Firebase Component: Any (Auth, Core, Database, Firestore, Messaging, Storage, etc)
* Target platform(s): `iOS`

### [REQUIRED] Step 2: Describe the problem

#### Steps to reproduce:

Trying to import `https://github.com/firebase/firebase-ios-sdk.git` in Swift Playgrounds as a Swift Package doesn't let me select any version or install it

#### Relevant Code:

```
// TODO(you): code here to reproduce the problem
```