set the parent state to connected if in open.

When opening a nested transaction when the parent is in state `open` I get the following error:

```
TypeError: Cannot call method 'bind' of undefined
    at OpenTransaction.Transaction._createChildTransaction (node_modules/any-db/lib/transaction.js:92:36)
    at OpenTransaction.begin (node_modules/any-db/lib/transaction.js:242:15)
```