Sub-key with multiline string value is parsed as key, not subkey

Hello,
this file :

```toml
key.sub = """
multiline string
"""
```

should be parsed as : 

```
{ 'key': 'sub': { 'multiline string\n' } }
```

but is instead parsed as: 

```
{'key': {}, 'sub': 'multiline string\n'}
```


