Unable to write plain text KEY property value

Code:

```java
VCard vcard = new VCard();

Key key = new Key();
key.setText("abracadabra", KeyType.GPG);
vcard.addKey(key);

Ezvcard.write(vcard).go(System.out);
```

Output:

```
BEGIN:VCARD
VERSION:3.0
PRODID:ez-vcard 0.10.5-SNAPSHOT
KEY:
END:VCARD
```