[Bug] FormSpy render method called multiple times with different values

### Are you submitting a **bug report** or a **feature request**?
Bug

### What is the current behavior?
When initialValues on form changes, the FormSpy don't recognize this update any more. So the values in the FormSpys render function gets the previous initialValues as parameter. This was working correct in 3.6.1 but broke in 3.6.2

### What is the expected behavior?
When intialValues of a form change, the FormSpy should also recognize this change and pass the new values to its render function.

### Sandbox Link

### What's your environment?

react 16.4.1
final form 4.8.2
react final form 3.6.2