Update MR diff blob_fork_suggestion after jQuery update

What does this MR do?

• Add BlobForkSuggestion.init() call to MR diff
  • .init() was introduced in the jQuery refactor, https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/10858
  • When https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/10868 and https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/10858 were merged side by side, we didn't have a conflict and it was an oversight to update this usage.

Are there points in the code the reviewer needs to double check?

Why was this MR needed?

• MR diff edit specs failing
  • https://gitlab.com/gitlab-org/gitlab-ce/builds/15001919

Does this MR meet the acceptance criteria?

• Tests
  • All builds are passing
• Conform by the merge request performance guides
• Conform by the style guides
• Branch has no merge conflicts with master (if it does - rebase it please)
• Squashed related commits together

cc @stanhu, https://gitlab.slack.com/archives/C02PF508L/p1493142827825506