[#243] Fix bug where data types and formats had no keys
[#243] Fix bug where data types and formats had no keys

This was throwing the following error:

```
Warning: Each child in an array or iterator should have a unique "key" prop.
```

Fixes #243

okfn/datapackagist,datapackages/datapackagist,datapackages/datapackagist,okfn/datapackagist