Fix comment-service-test.js

Fix comment-service-test.js

npm run mocha -- modules/topics/test/comment-service-test.js

---

Before:

comment-service #slow
2018-05-04T00:20:38.993Z - info: Indices configured
{ category: 'persistence' }
    1) "before all" hook


  0 passing (2s)
  1 failing

  1) comment-service #slow "before all" hook:
     Error: timeout of 2000ms exceeded. Ensure the done() callback is being called in this test.
      at Timeout.<anonymous> (C:\Users\MLM\Documents\GitLab\webapp\node_modules\mocha\lib\runnable.js:226:19)

After:

comment-service #slow
2018-05-04T00:23:25.842Z - info: Indices configured
{ category: 'persistence' }
    √ should add a comment (1675ms)
    √ should update a comment's text
    √ should delete a comment


  3 passing (2s)