Discussion student vote throws error

1. Author a Discussion component and enable "Students can vote on posts"
2. Sign in as a student and try to upvote or downvote a reply by another student
3. Nothing happens and you will see this error in the console

```
ERROR TypeError: this.createdownvoteannotation is not a function
    at ClassResponse.downvoteClicked (class-response.component.ts:226:12)
```