Collection data imgs: ipfs should be changed to string

I get this error using the example provided for `setCollectionData`

```
UnhandledPromiseRejectionWarning: Error: type "ipfs" is not valid for variant
```

Please replace:

```
{"key": "img", "value": ["ipfs", "somehash"]},
```

With:

```
{"key": "img", "value": ["string", "somehash"]},
```