Fixed _get_key returning prematurely

Fixed _get_key returning prematurely

Variables were clobbering other variables... badness was happening.

When given
```test.ms
{{# container }}
  {{ sibbling.child }}
{{/ container }}
```

```test.json
{
    "container": [1,2,3],
    "sibbling": {
        "child": "Just me."
    }
}
```

it was returning
```wrong.txt
  {'child': 'Just me.'}
  {'child': 'Just me.'}
  {'child': 'Just me.'}
```

when it should have returned
```right.txt
  Just me.
  Just me.
  Just me.
```