Changed the numberOfTimesThenWasRetrieved to be added when 'then' is cal...

To detect whether an object is 'thenable', a Promise library needs to check whether 'then' is callable.
This check would be something like below:
```
if (obj && typeof obj.then === 'function') {
  // thenable
  obj.then(f1, f2);
}
```
In this case, 'then' will be referred to twice (numberOfTimesThenWasRetrieved === 2)
However, these test cases require numberOfTimesThenWasRetrieved to be 1.
I think numberOfTimesThenWasRetrieved must be the times 'then' is called rather than 'then' is referred to.