Fixed rule.imp() undefined is not a function error

Hello I am getting this error with the current version of Fez:

```
fez/src/main.js:84
    done = new Promise.resolver();
           ^
TypeError: undefined is not a function
```

I fixed it by replacing what I assume is old Bluebird code. I replaced the callback with the one provided by PromiseResolver. I think this is better because errors can be passed in the traditional node callback sense, however maybe it doesn't matter.